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##

MINNESOTA STATEWIDE MERCURY 

TOTAL MAXIMUM DAILY LOAD 

Final* 

March 27, 2007 

 *Approved by US EPA March 27, 2007 

wq-iw4-01b 
wq-iw4-01b 
Contents 

Contents ........................................................................................................................................................i

Tables ..........................................................................................................................................................iv

Figures.........................................................................................................................................................iv

Acknowledgements .....................................................................................................................................v

Executive Summary ...................................................................................................................................vi

Abbreviations .............................................................................................................................................xi

Definition of Terms...................................................................................................................................xii

1 Introduction.........................................................................................................................................1

2 Background Information....................................................................................................................2

2.1 Mercury Cycle .............................................................................................................................2

2.2 Data Collection and Assessment .................................................................................................2

2.3 Other State and Federal Regional Mercury TMDLs ...................................................................3

3 Applicable Water Quality Standards................................................................................................4

3.1 Mercury Numeric Water Quality Standards................................................................................4

3.2 Fish Consumption Advisory........................................................................................................5

3.3 Basis for Assessment of Fish Contaminants – Narrative Standards............................................6

3.3.1 Minnesota Rule Chapter 7050.................................................................................................6

3.3.2 Selection of Single Fish Meal-Per-Week Impairment Threshold ...........................................6

3.3.3 Fish Tissue Criterion for Mercury...........................................................................................7

4 Minnesota’s Regional Approach........................................................................................................7

4.1 Land Cover and Water Quality....................................................................................................7

4.2 Ecoregions ...................................................................................................................................8

4.3 Baseline Year: 1990.....................................................................................................................9

4.4 Target Levels of Fish Mercury Concentration...........................................................................11

4.4.1 Standard Size Predator Fish ..................................................................................................11

4.4.2 Applying the Target Level to the 90th Percentile Fish Concentration ...................................13

4.4.3 Achieving Water Quality Criteria for Mercury.....................................................................18

5 Source Assessment and Trends........................................................................................................18

5.1 Sources of Mercury in Minnesota Fish......................................................................................18

i
5.2 Principle of Proportionality for Mercury in Air and Biota ........................................................23

5.3 Trends in Mercury Emissions and Deposition...........................................................................26

5.3.1 Trends in Use and Emission of Mercury...............................................................................26

5.3.2 Trends in Atmospheric Deposition of Mercury ....................................................................29

5.4 Interaction Between Sulfate Deposition and Mercury Methylation ..........................................30

5.5 Point Sources to Water ..............................................................................................................31

5.6 Environmental Trends ...............................................................................................................32

5.6.1 Summary of Scientific Information.......................................................................................32

5.6.2 Predicting Response Time.....................................................................................................33

5.6.3 Trends in Fish Contamination...............................................................................................33

6 TMDL Development .........................................................................................................................35

6.1 TMDL Formulation ...................................................................................................................35

6.2 Baseline Mercury Load for 1990...............................................................................................35

6.3 Wasteload Allocations (WLA) ..................................................................................................37

6.4 Load Allocations (LA)...............................................................................................................38

6.5 Reserve Capacity .......................................................................................................................40

7 Margin of Safety................................................................................................................................40

8 Seasonal Variation and Critical Conditions ...................................................................................41

9 Final TMDL.......................................................................................................................................41

10 Monitoring & Research Plan ...........................................................................................................42

11 Projected Implementation................................................................................................................42

11.1 Background................................................................................................................................42

11.2 General Approach......................................................................................................................42

11.3 Implementation for Wasteload Allocation.................................................................................43

11.4 Implementation for Load Allocation .........................................................................................44

11.4.1 Short-term Actions ................................................................................................................45

11.4.2 Reduction Targets and Milestones ........................................................................................46

11.4.3 Regulatory Actions................................................................................................................47

12 Reasonable Assurance ......................................................................................................................47

12.1 Assurances Occur at Multiple Levels........................................................................................47

12.2 State Level Assurances..............................................................................................................47

12.3 National and International Assurances ......................................................................................50

13 Public Participation ..........................................................................................................................51

14 References..........................................................................................................................................52

ii
Appendix A Impaired Waters Covered by the Statewide Mercury TMDL

Appendix B NPDES Permits Covered by the Statewide Mercury TMDL

iii
Tables 

Table ES- 1 Summary of Minnesota's Regional Mercury TMDLs...........................................................viii

Table 1 Fish Tissue Mercury Concentrations for MDH’s Levels of Consumption Advice.........................5

Table 2 Regional Differences in Land Cover and Water Quality.................................................................9

Table 3 Mercury Concentrations for Northern Pike (NP) and Walleye (WE) Collected from 1970 to 2002

............................................................................................................................................................14

Table 4 Mercury Concentrations Standard Size Northern Pike and Walleye for 1988-1992 ....................16

Table 5 Reduction Factors Based on the Baseline Year: 1990 ..................................................................17

Table 6 Bioaccumulation factors for 14 representative lakes in Minnesota ..............................................18

Table 7 Mercury Load Inputs and Estimates for 1990...............................................................................36

Table 8 Mercury Load Reductions for Each Region .................................................................................38

Table 9 Mercury Load Allocation for In-State and Out-of-State Emissions .............................................39

Table 10 Minnesota’s Mercury TMDL Emissions Reduction Goal ..........................................................40

Table 11 WWTP Mercury Reduction Plan ................................................................................................43

Table 12 Summary of Reduction Targets ..................................................................................................46

Table 13 Summary of Mercury Reduction Strategies Used in Minnesota Since 1990...............................48

Table 14 Summary of Regional, National and International Mercury Reduction Initiatives .....................51

Figures 

Figure ES- 1 Minnesota's 2004 Impaired Waters by Pollutant...................................................................vi

Figure ES- 2 TMDL Regional Areas and Mercury-Impaired Waters........................................................vii

Figure 1 Impaired Waters by Pollutant for 2004 303(d) List.......................................................................1

Figure 2 TMDL Regional Areas and Mercury-Impaired Waters...............................................................10

Figure 3 Average Fish Tissue Mercury Concentration Greater Than 0.2 ppm by Species and Size Class

............................................................................................................................................................12

Figure 4 Size Class Distributions by Region (NE, SW) and Species (NP, WE) ........................................13

Figure 5 Standard size northern pike and walleye distribution..................................................................15

Figure 6 Mercury Distributions by Species and Region for 1988-1992 ....................................................16

Figure 7 Upper percentiles for northern pike (NP and walleye (WE) in the NE, SW, and Metro Regions

............................................................................................................................................................17

Figure 8 Annual Mercury Flux at Mercury Deposition Network (MDN) Sites in Minnesota...................21

Figure 9 Sources of Mercury Deposition and Estimated Mercury Emission Sources in Minnesota .........22

iv
Figure 10 Proportionality between atmospheric mercury deposition and mercury concentrations as 

predicted by the E-MCM model for largemouth bass in the Everglades............................................24

Figure 11 Mercury Consumption in the United States...............................................................................27

Figure 12 United States Mercury Emissions by Category.........................................................................27

Figure 13 Minnesota Statewide Mercury Emissions Trend by Source......................................................28

Figure 14 USEPA's anthropogenic mercury emissions in U.S. .................................................................29

Figure 15 Mercury Accumulation Record in the Fremont Glacier, Wyoming ..........................................30

Figure 16 Predicted Dynamic Responses of Fish Tissue Mercury Concentrations Following Reductions 

in Mercury Deposition ........................................................................................................................33

Figure 17 Comparison Between Recent and Historical Fish Mercury Levels in 176 lakes (Northern Pike 

and Walleye; Standard Lengths).........................................................................................................34

Figure 18 Proportional relationship between mercury deposition and fish mercury concentration in the 

two TMDL regions .............................................................................................................................38

Acknowledgements 

The Minnesota Pollution Control Agency acknowledges the important contribution of the many 

stakeholders that have participated in Minnesota’s Mercury Reduction Initiative and the Impaired Waters 

Program. We appreciate the support and encouragement of the USEPA’s Region 5 and Headquarters 

staff. The main contributors to this mercury TMDL are the Mercury TMDL Project Technical 

Committee: Howard Markus, Bruce Monson, Edward Swain, Ned Brooks, and Anne Jackson. 

v
vi

Executive Summary 

Mercury is a neurotoxin, meaning it damages the central nervous system. The developing nervous system 

is at the greatest risk for damage. Mercury is also a global pollutant; it is transmitted around the world 

and accumulates to levels in fish that are potentially toxic to humans and wildlife. This report sets a 

target for fish tissue concentration of mercury that is generally safe for human consumption, and 

translates the target to reduction goals for mercury sources. 

Environmental contaminants are usually treated as media-specific—an air, water, or soil contaminant. 

Mercury is a multimedia pollutant: transported by air, stored in soil, and chemically transformed and 

bioaccumulated in water. Mercury reductions needed to achieve the target for safe fish consumption are 

translated to mercury emissions reductions, because 99 percent of mercury load to Minnesota’s lakes and 

streams is from atmospheric deposition. 

Because this report includes jargon from the Clean Water Act and the Clean Air Act, the following point 

of clarification is needed: this report will refer to water releases of mercury as “discharges” and air 

releases as “emissions.” While stacks from air emission sources may be referred to as point sources in the 

air-permitting arena, the Total Maximum Daily Load (TMDL) concept arises from the Clean Water Act, 

where “point sources” refer to identifiable pipe conveyances and include wastewater and stormwater, 

which have National Pollutant Discharge Elimination System (NPDES) permits. Therefore, air sources 

(i.e., stacks) will be referred to as “point source emissions” and water sources (i.e., pipes) will be referred 

to as “point source discharges.” 

Impaired Waters List Section 303(d) of the Federal Clean Water Act requires every state to prepare a 

list of impaired waters. Minnesota’s 2004 303(d) List (“Impaired Waters List”) includes water quality 

impairments in 1892 lakes and river reaches. Two-thirds of those waters are impaired because of mercury 

(Figure ES- 1). The 1239 impairments by mercury consist of 820 lake impairments and 419 river 

impairments. Twelve lakes and 20 river reaches are impaired for mercury in fish tissue and in the water 

column; 808 lakes and 399 river reaches are impaired for fish tissue only. 

Impaired Waters, 2004

Low DO, 45, 2%

Other PBTs, 129, 7%

Excess nutrients, 

153, 8%

Ammonia, 10, 1%

Biotic community, 

103, 5%

Mercury, 1239, 

66%

River Impairments, 

419, 22%

Lake Impairments, 

820, 44%

Others (pH, T., Cl), 

6, 0%

Turbidity, 118, 6%

Fecal coliform, 

89, 5%

Figure ES- 1 Minnesota's 2004 Impaired Waters by Pollutant 

Each impaired water is required to have a total maximum daily load study (TMDL). The TMDL is an 

evaluation of (1) pollutant sources, (2) pollutant load reduction needed to meet water quality standards 

and (3) allocation of the acceptable load to all sources. Because the source of essentially all mercury in 

Minnesota waters is atmospheric and, therefore, shared by all mercury-impaired waters of the state, the 
pollutant allocation to atmospheric sources will be the same for these waters. Seventy percent of 

atmospheric mercury deposition is from anthropogenic sources (i.e., from human activities) and the 

remaining thirty percent is from natural sources, such as volcanoes. Although state waters share common 

mercury sources, their capacity to assimilate the pollutant load varies because of differences in 

geography, water chemistry, and food webs. These differences are apparent in the geographic variation of 

mercury concentrations in fish, which is addressed through a regional approach. 

Regional Approach The state is divided into two regional mercury TMDLs: northeast (NE) and a 

southwest (SW). The the two regions are separated by ecoregion boundaries (Figure ES- 2); NE 

comprises 41% of the state and SW covers 59%. Land-water mercury transport processes and 

concentrations in fish differ between the two regions. Land cover and geology controls transport 

processes and, consequently, water quality. NE region is dominated by forest and wetlands, and SW 

region is dominated by cultivated lands. Because there are similarities and differences between the two 

regions, the regional mercury TMDLs were developed (and described) in parallel. 

Northern Lakes and Forests

Northern 

Minnesota 

Wetlands

Red 

River 

Valley

North Central 

Northern Hardwood Forest

Glaciated 

Plains

Western Corn 

Belt Plains Driftless 

Area

TMDL Regional Area

Northeast (NE)

Southwest (SW)

Minnesota Pollution

Control Agency

Impaired waters 

are highlighted

Figure ES- 2 TMDL Regional Areas and Mercury-Impaired Waters 

TMDL Development The TMDL development follows a series of logical scientifically-based steps, 

beginning with establishment of the regional target level or endpoint goal (Table ES- 1). Both regions 

have the same fish tissue target level; however, because fish mercury concentrations differ by region, the 

vii
Table ES- 1 Summary of Minnesota's Regional Mercury TMDLs 

This table summarizes the six steps to develop Minnesota’s Mercury TMDL. See referenced report sections for more information about each step. 

Regional Area in Minnesota 

(1) The State is divided into two regions—Northeast (NE) and Southwest (SW)—based on differences in mercury’s movement through the environment and fish tissue concentrations. [Section 4] Percent of total state area 

Target Level and Reduction Factor 

Target fish mercury concentration Mercury concentration for standard length walleye (WE4090) 

(2) The TMDL target is the water quality criterion for mercury in fish. The 90th percentile fish tissue mercury concentration for a standard length walleye (40 cm) is compared to the fish tissue mercury criterion. The Reduction Factor is the percent reduction needed for fish to meet the water quality criterion. [Section 4.4] Reduction Factor [RF=(WE4090 - 0.2)/WE4090] 

Mercury Load for Baseline Year – 1990 

Point Source Load (PSL; wastewater discharge) 

PSL percent of Total Source Load 

Nonpoint Source Load (NPSL; atmospheric deposition) 

(3) Loads from mercury sources are summed by region for the 1990 mercury load that was either discharged from wastewater or deposited from air emissions. About 99% of the statewide mercury load was from nonpoint (air) sources in 1990. Nonpoint source load is the product of atmospheric deposition (12.5 grams per square kilometer per year) and regional area. Wastewater sources contribute about one percent of the total load in 1990 [Section 6.2][1] Total Source Load (TSL) 

Final TMDL 

Mercury TMDL Loading Goal [TSL• (1– RF)] Wasteload Allocation (WLA) 

(4) The Mercury TMDL is a loading goal equal to 1990 Total Source Load multiplied by (1- Reduction Factor), and is equal to wasteload allocation (WLA) plus load allocation (LA). The WLA consists of water point source discharges; it is set at one percent of the TMDL or equal to the estimated point source load, whichever is lower. The remainder of the TMDL is LA, which are atmospheric deposition sources. [Section 9][2] Load Allocation (LA) 

Mercury Load Allocation for In-state and Out-of-state Deposit

In-State contribution to LA [0.143•LA) Out-of-State contribution to LA [(1-0.143)•LA] Mercury TMDL Atmospheric Deposition Goal 

(5) To achieve the Mercury TMDL Goal, all load reductions must come from anthropogenic sources, which are 70% of the total atmospheric mercury deposition and are divided into in-state and out-of-state emission sources. In-state emission sources contribute 10% of the total mercury deposition, or 14.3% of the anthropogenic sources. The load is allocated to in-state and out-of-state contributions for both regions. The TMDL goal is converted to a mercury deposition flux (g km-2 yr-1) when divided by the 

regional area. [Section 6.4] Necessary reduction from anthropogenic emission sources (RF ÷ 0.7) 

Minnesota's Mercury TMDL Emissions Reduction Goal 

State's mercury emissions for 1990 Emissions Reduction Goal (0.93 •1990 Emissions) 

Minnesota's TMDL Mercury Emissions Goal (1990 Emissions – Reduction Goal) 

Emissions reductions as of 2005 (70% of 1990 emissions) Emissions reduction remaining as of 2005 to achieve goal 

(6) Because atmospheric mercury deposition is uniform across the entire state and in-state emissions disperse across both regions, the greater reduction goal, established for the northeast, becomes the statewide mercury load reduction goal, which is a 93% reduction in anthropogenic emissions. Subtracting the emissions reduction goal from the 1990 state emissions gives the state’s TMDL mercury emissions goal. Since this TMDL uses 1990 as the starting point, it is informative to determine progress the state has made from 1990 to 2000. Between 1990 and 2005, 76% of the mercury emissions reduction goal was achieved, leaving 24% still to be met. [Section 6.4] Percent of 1990 Emissions Reduction Goal remaining as of 2[1] For discussion of Reserve Capacity see Section 6.5[2] For discussion of Margin of Safety see Section 7 [3] Minnesota’s mercury deposition sources are 30% natural and 70% anthropogenic. The anthropogenic share is comprised of 30% global and 40% regional so

is from sources within Minnesota; therefore, the state’s anthropogenic sources are 10% of total deposition (0.25 * 0.4). There are no significant natural sources mineral ores) in Minnesota. Mercury in Minnesota’s soils is from atmospheric deposition. 
ix

necessary load reductions to achieve the goal differ by region. Minnesota’s target level for mercury in 

fish is 0.2 mg/kg (parts per million, ppm), based on the EPA’s development of a methylmercury criterion 

for fish tissue to protect human health. Minnesota’s fish tissue mercury criterion is lower than EPA’s 0.3 

ppm criterion because of the higher fish consumption rate in the state. The 0.2 ppm corresponds to the 

Minnesota fish consumption advisory threshold for one meal per week—above that mercury concentration the consumption advice is one meal per month—for women who are pregnant or intending to become 

pregnant and children under 15 years of age. 

Load reductions must be calculated relative to an appropriate baseline annual load. The most recent 

research that establishes total mercury deposition in Minnesota took place from 1988 to 1990. In 

addition, a baseline year of 1990 for this TMDL corresponds to the baseline year for Great Lakes mercury 

reduction goals and Minnesota’s mercury emissions reduction goals. Prior to 1990 mercury use was 

relatively high and dropped precipitously beginning around 1990 as mercury was removed from many 

common products. Mercury deposition and mercury in fish tissue were probably in a relative steady state 

through 1990; therefore, comparing mercury deposition and fish tissue concentration in 1990 is most 

likely valid because of the steady state conditions leading up to 1990, but we have since entered a nonsteady state period as mercury deposition declines. 

For these regional TMDLs, target levels of mercury concentrations were determined in standard size top 

predator fish: northern pike (Esox lucius) and walleye (Sanders vitreus). Because mercury bioaccumulates and biomagnifies, concentration is highest at the top of the food web; therefore, achieving the 

mercury target concentration in the top predator fish will result in the whole food web, including the 

water column, achieving the target level. For the 1990 baseline year, fish tissue data were combined for 

each region for a five-year period—1988 to 1992—to account for annual weather fluctuations. 

The target level of 0.2 ppm was applied to the 90th percentile mercury concentration. By protecting for 

the 90th percentile we expect to achieve the target level for other biota and for water concentrations of 

mercury. The difference between the regional 90th percentile concentration for the standard size fish and 

0.2 ppm is the reduction factor (RF) needed to meet water quality standards. The RF is greater for the NE 

than the SW for both walleye and northern pike. Mercury concentrations in walleye were slightly higher 

than northern pike levels in both regions and, therefore, the RF for walleye was selected for load 

reduction calculations to provide a margin of safety. The resulting RFs are 65% for the NE and 51% for 

the SW. 

The total source load (TSL) is the sum of the point source loads (PSL) and the non-point source loads 

(NPSL). Point source loads include the NPDES permitted facilities in the state, excluding cooling water 

discharges. PSL for the region is the product of facility design flow and the average measured effluent 

mercury for wastewater treatment plants in the state (5 ng Hg/L). Non-point source load is the product of 

atmospheric deposition flux in 1990 (12.5 g km-2 yr-1) and regional surface area. The subsequent 1990 

TSLs for NE and SW regions were 1153 kg/y and 1628 kg/y, respectively. About one percent of the TSL 

is attributable to PSL. 

Mercury TMDL Goal for Minnesota Total mercury deposition in 1990 was 12.5 g km-2 yr-1 throughout 

the state. To achieve the target levels in fish tissue, the mercury deposition goals are 4.4 g km-2 yr-1 for 

the NE and 6.1 g km-2 yr-1 for the SW. 

Mercury load reduction goals for each regional TMDL were calculated by applying the RF to the baseline 

mercury load. Reductions can only come from anthropogenic sources; therefore, load reduction goals 

require anthropogenic source reductions of 93% (65% reduction goal divided by 70% of total that is 

anthropogenic) in the NE region and 73% (51% of reduction goal divided by 70% anthropogenic) in the 

SW region. 

Ten percent of the mercury deposition is attributed to anthropogenic sources within the state. Since 

natural sources cannot be controlled and are not expected to change, all mercury reductions must come 
from anthropogenic sources. The state’s percentage of the anthropogenic sources is 14.3% (10% of total 

divided by 70% of total). The state’s contributions to the load allocations (LA) are 0.16 kg/d for the NE 

and 0.31 kg/d for the SW. The out-of-state contributions to the LA are 0.94 kg/d for the NE and 1.86 

kg/d for the SW. 

Mercury Emission Reduction Goals Mercury load reduction goals are applied to emission reductions 

for the state. Atmospheric deposition of mercury is considered uniform across the state, and in-state 

emissions disperse across both regions; therefore, the emissions goal is applied statewide rather than by 

region. The northeast’s greater regional reduction goal (i.e., 93% of anthropogenic sources) determines 

the TMDL’s emission reduction goal. In 1990, the total mercury emissions from in-state sources were 

11,272 lbs (5513 kg); the TMDL emissions goal is seven percent of the 1990 emissions: 789 lbs (358 kg). 

Minnesota’s 1990 mercury emissions were reduced 70% by 2005, which is equivalent to 76% statewide 

emissions reduction goal, leaving 24% of the emissions reductions goal remaining. Going from 3,341 lbs 

mercury emissions in 2005 to the emissions goal of 789 lbs constitutes another 76% reduction in mercury 

emissions. 

TMDL Implementation To achieve the mercury reductions goals, Minnesota will develop a detailed 

implementation plan. An implementation plan is not required in a TMDL; it is developed after the TMDL 

plan is approved by the USEPA. A section on projected implementation is included in this report to 

inform the public and to aid in the discussion on reasonable assurance. The implementation and 

reasonable assurance sections summarize initiatives that the MPCA believes have already reduced fish 

contamination in Minnesota and will maintain a path of reduced fish contamination in the future. 

Although wastewater point sources are very minor contributors to the total mercury load, the MPCA will 

continue to pursue mercury reductions from these sources through mercury minimization plans and other 

permit conditions. For mercury emission sources, sector-specific reduction milestones are presented, 

along with an outline of regulatory and non-regulatory mercury reduction strategies to be considered in 

the detailed implementation planning. The Great Lakes Initiative (GLI) requires wastewater dischargers 

in the Lake Superior basin to meet a mercury water quality standard of 1.3 ng/L and implementation of 

this mercury TMDL does not in any way supercede or conflict with the GLI requirements. 

x
xi

Abbreviations 

# - number 

% - percent 

A – area 

b – bioavailability factor 

C – mercury concentration 

Cl – chloride 

Dy – annual air deposition of mercury 

d – day 

DA – Driftless Area ecoregion 

DDT – dichlorodiphenyltrichloroethane 

ECOS – Environmental Council of States 

EPA – US Environmental Protection Agency 

EU – European Union 

FCA – fish consumption advisory 

g – gram 

Hg – mercury 

kg – kilogram 

km – kilometer 

Lair – air deposition mercury load 

L – liter 

LA – load allocation 

LaMP – Lake area Management Plan 

lb – pound 

MACT – Maximum Achievable Control 

Technology 

MDH – Minnesota Department of Health 

MDNR – Minnesota Department of Natural 

Resources 

Metro – the Twin Cities Metropolitan Area 

MFCA – Minnesota Fish Consumption 

Advisory 

mg – milligram 

Minn R ch – Minnesota Rules Chapter 

Minn R p – Minnesota Rules part 

MMP – mercury minimization plan 

MOS – margin of safety 

MPCA – Minnesota Pollution Control Agency 

NCHF – North Central Hardwood Forest 

ecoregion 

NE – northeast 

ng – nanogram 

NGP – Northern Glaciated Plains ecoregion 

NLF – Northern Lakes and Forests ecoregion 

NMW – Northern Minnesota wetlands 

ecoregion 

NP55 – standard length Northern Pike – 55 cm 

NPDES – National Pollutant Discharge 

Elimination System 

NPSL – nonpoint source load 

PCBs – polychlorinated biphenyl compounds 

POPs – persistent organic pollutants 

ppm – parts per million 

PSL – point source load 

Q – flow 

r – runoff coefficient or delivery ratio 

RF – reduction factor 

RRV – Red River Valley ecoregion 

SA – surface area 

SRB – sulfate reducing bacteria 

Subp – subpart 

SW – southwest 

T – temperature 

TSL – total source load 

TMDL – Total Maximum Daily Load 

USGS – United States Geological Survey 

WCBP – Western Corn Belt Plains ecoregion 

WE40 – standard length Walleye – 40 cm 

WLA – wasteload allocation 

WQS – water quality standards 

WWTP – wastewater treatment plant 

yr – year 
Definition of Terms 

Air Sector – sources that emit wastes into the air 

Anthropogenic Mercury Emissions – the mobilization or release of geologically-bound mercury by human activity 

that results in a mass transfer of mercury to the atmosphere. 

Atmospheric deposition – the mass transfer of gaseous, aerosol, or particulate contaminant from the atmosphere to 

the earth’s surface (see mercury dry deposition and mercury wet deposition) 

Bioaccumulation – increase in contaminant concentration through a food web; includes uptake through food and 

water or air. Bioconcentration refers to uptake only through the water or air, not food. Biomagnification is increase 

in contaminant concentration between trophic levels. 

Chlorophyll-a – a pigment in green plants, including algae. The concentration of chlorophyll-a, expressed in 

weight per unit volume of water, is a measurement of the abundance of algae. 

de minimis – insignificant; reference to the phrase de minimis non curat lex: “The law does not concern itself with 

trifles;” - a principle of law, that even if a technical violation of a law appears to exist according to the letter of the 

law, if the effect is too small to be of consequence, the violation of the law will not be considered as a sufficient 

cause of action, whether in civil or criminal proceedings. For the mercury TMDL, wastewater point sources are 

considered de minimis if they represent less than one percent of the TMDL of mercury to the region. 

Dystrophic – a high concentration of dissolved humic organic matter in the water, causing the water to have a 

brown color; also, typically low in nutrients. 

Ecoregion – an area of relative homogeneity in ecological systems based on land use, soils, land and surface form, 

and potential natural vegetation. 

Fish consumption advisory – guidelines issued by Minnesota Department of Health for how often certain fish can 

be safely eaten, based on the data collected in Minnesota’s fish contaminant monitoring program. 

Global Scale – refers to emissions transported on a global scale; it does not refer to the sum of all emissions on 

Earth, but rather that portion of total emissions that are transported around the globe. 

Great Lakes Initiative (GLI) – the Great Lakes Water Quality Initiative required states in the Great Lakes region 

to adopt strict water quality standards for bioaccumulative chemicals of concern, which includes a mercury water 

quality standard of 1.3 ng/L. Minn. R. ch. 7052 codified the GLI requirements and is, therefore, referred to in 

Minnesota as the GLI rule.

Half-life – The time required for the amount of a substance to decrease to half its initial value (see Residence Time). 

Hot spot – refers to a mercury concentration in fish or water that is obviously (1) higher than other concentrations in 

the area and (2) caused by a local source. 

Impaired water – a water body that does not meet applicable water quality standards or fully support applicable 

beneficial uses, due in whole or in part to water pollution from point or nonpoint sources, or any combination 

thereof. 

LaMP – Lake areawide Management Plan – a watershed management plan required for each of the Great Lakes. 

Local scale – A relative term, used to describe the area within which emissions can travel in one diurnal cycle 

(generally within 100 km of a source). Local influences are characterized by measurable concentration gradients 

with relatively large fluctuations in air concentrations caused by meteorological factors such as wind direction 

(Expert Panel 1994) 

Lognormal – a variable, such as mercury concentration in fish, that has a skewed distribution (median is much 

lower than the mean), but the logarithms of the values have more of a normal distribution (mean and median are 

approximately equal). 

MACT – Maximum Achievable Control Technology—a pollution regulatory program administered through the 

USEPA. 

Mechanistic model – a computer model that is based on known physical, biological, and chemical processes. 

Mercury dry deposition – mass transfer of gaseous, aerosol, or particulate mercury species from the atmosphere to 

the earth’s surface (either aquatic or terrestrial, including trees and other vegetation) in the absence of precipitation. 

xii
Mercury wet deposition – mass transfer of dissolved gaseous or particulate mercury species from the atmosphere 

to the earth’s surface (either aquatic or terrestrial) by precipitation. 

Methylation (Methylated) – process of adding a methyl (CH3

-

) group to a mercury ion (Hg2+). Methylation can 

occur either biotically or abiotically, but sulfate-reducing bacteria are considered the primary methylators in aquatic 

systems (i.e., wetlands and lakes). 

Methylmercury – CH3Hg+

 or MeHg – a cation that is the biologically active form of mercury; it has a very high 

affinity for sulfur-containing compounds, such as the amino acid cysteine; this is the form of mercury that 

accumulates in fish and is toxic to humans and wildlife. 

National – for the purposes of this TMDL, national is the United States except Minnesota; thus, mercury emission 

sources include Minnesota sources, national sources, global sources, and natural sources. 

Natural mercury emissions – mobilization or release of geologically-bound mercury by natural biotic and abiotic 

processes that result in mass transfer of mercury to the atmosphere. 

Nonpoint sources – diffuse sources of pollution to water from land use or atmospheric deposition of pollutants. 

Oligotrophic – low nutrient concentration, resulting in low plant and animal productivity. Many lakes in northern 

Minnesota are oligotrophic. The contrasting condition is eutrophic – high nutrient concentration and biological 

productivity. 

Point sources – wastewater discharges and all other pollutant sources that enter the receiving water through a pipe 

or channel. 

Reference Dose (RfD) – an estimate of a daily oral exposure to the human population (including sensitive 

subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. 

Regional scale – a relative term, defining that area requiring more than one diurnal cycle emission transport time 

(about 100 to 2000 km from a source). The regional scale describes areas sufficiently remote or distant from large 

emission sources so that concentration fields are rather homogeneous, lacking measurable gradients (Expert Panel 

1994). 

Reserve capacity – pollutant load allocation to account for uncertainty and future growth. 

Residence time - average time that a substance resides in a designated area (e.g., atmosphere or water body). 

Standard length fish – a set total fish length that is used to compare mercury concentrations among lakes and over 

time. The standard lengths used by the MPCA are 55 cm northern pike (NP55) and 40 cm walleye (WE40). 

Mercury concentrations for a standard length fish are determined from a linear regression of measured mercury fish 

tissue concentration versus fish length. 

Steady state – occurs when there is a balance between inflows and outflows of a system; also referred to as dynamic 

equilibrium; for the mercury TMDL, this refers to a condition when inflows and outflows are not changing rapidly 

with respect to changes fish tissue concentrations, which can take 5-10 years to respond to changes in mercury load. 

Taconite – low-grade iron ore processed by crushing and concentrating to yield a pellet for use in iron smelters. 

Taconite has low mercury concentrations but large volumes of the material are heated during processing, which 

releases significant quantities of mercury into the atmosphere. 

TMDL – Total Maximum Daily Load. The maximum amount of a pollutant that a waterbody can receive and still 

meet water quality standards. TMDL also refers to the process of allocating pollutant loadings among point and 

nonpoint sources. 

xiii
MN Statewide Mercury TMDL 27MAR07_final.doc 1

1 Introduction 

Mercury is a toxic pollutant and eating mercury-contaminated fish is the primary route of exposure for most 

people and wildlife. Mercury has accumulated in fish throughout the world because of human activities that emit 

mercury to the environment. Even lakes in natural pristine areas contain fish with high mercury concentrations, 

because mercury is deposited from the atmosphere and can travel long distances from its emission source. 

Two thirds of the waters on Minnesota’s 2004 Impaired Waters List are impaired because of mercury 

concentrations in fish or water (Figure 1). Waters are listed as impaired if mercury in fish tissue is greater than 

0.2 ppm, which corresponds to a fish consumption advisory threshold for sensitive populations1

 that is more 

restrictive than one meal per week. Waters are also listed as impaired if mercury in water exceeds the water 

quality standard for mercury: 1.3 ng/L in the Lake Superior Basin and 6.9 ng/L elsewhere in the state. The 1239 

impairments by mercury consist of 820 lake impairments and 419 river impairments. Twelve lakes and 20 river 

reaches are impaired for mercury in fish tissue and in the water column; 808 lakes and 399 river reaches are 

impaired because of fish tissue only. 

Impaired Waters, 2004

Low DO, 45, 2%

Other PBTs, 129, 7%

Excess nutrients, 

153, 8%

Ammonia, 10, 1%

Biotic community, 

103, 5%

Mercury, 1239, 

66%

River Impairments, 

419, 22%

Lake Impairments, 

820, 44%

Others (pH, T., Cl), 

6, 0%

Turbidity, 118, 6%

Fecal coliform, 

89, 5%

Figure 1 Impaired Waters by Pollutant for 2004 303(d) List 

To ensure the continued good health of people that eat fish in Minnesota, the MDH issues guidelines—Minnesota 

Fish Consumption Advisory (MFCA)—for how often certain fish can be safely eaten (MDH 2004). The MFCA 

is strictly advisory, the goal being to help people that eat fish make intelligent decisions on which fish to eat and 

which to avoid. In contrast, the 303(d) [Impaired Waters] List identifies waterbodies that do not meet legally 

enforceable water quality standards, requiring a study of the total maximum daily load (TMDL) that is necessary 

to meet the water quality standard. 

This report describes the statewide, regional approach that Minnesota has taken to developing total maximum 

daily loads for mercury. The two regions—Northeast and Southwest—provide clear distinctions for assessing 

mercury loads to surface waters based on differences between the regions in watershed transport processes and 

mercury bioavailability.

 

1

 Women who are pregnant or intending to become pregnant and children under 15 years old. 
2 Background Information 

2.1 Mercury Cycle 

Mercury has unique properties as a multi-media pollutant, cycling through the air, water, land, and biota. The 

Mercury Study Report to Congress (USEPA 1997) gave the following summary of the mercury cycle: 

Mercury cycles in the environment as a result of natural and human (anthropogenic) activities. The amount of 

mercury mobilized and released into the biosphere has increased since the beginning of the industrial age. Most 

of the mercury in the atmosphere is elemental mercury vapor, which circulates in the atmosphere for up to a year, 

and hence is widely dispersed and transported thousands of miles from the likely sources of emission. Most of the 

mercury in water, soil, sediments, or plants and animals is in the form of inorganic mercury salts and organic 

forms of mercury (e.g., methylmercury). The inorganic form of mercury, when either bound to airborne particles 

or in a gaseous form, is readily removed from the atmosphere by precipitation and is also dry deposited. ... 

Even after it deposits, mercury commonly is emitted back to the atmosphere either as a gas or associated with 

particles, to be re-deposited elsewhere. As it cycles between the atmosphere, land, and water, mercury undergoes 

a series of complex chemical and physical transformations, many of which are not completely understood. 

Mercury accumulates most efficiently in the aquatic food 

web. Predatory organisms at the top of the food web 

generally have higher mercury concentrations. Nearly all 

the mercury that accumulates in fish tissue is methylmercury. Inorganic mercury, which is less efficiently 

absorbed and more readily eliminated from the body than 

methylmercury, does not tend to bioaccumulate.

2.2 Data Collection and Assessment 

This section describes how data are collected and assessed 

for possible inclusion in the 303(d) list. Essentially all of 

the discussion is excerpted from the MPCA TMDL 

guidance document (MPCA 2004a). 

A link in the aquatic food chain: a walleye 

pursuing a yellow perch 

The MPCA uses data collected over the most recent 10-year period for all the water quality assessments, except in 

the case of fish contaminated with mercury. There is no age limit for the use of mercury fish tissue data, for the 

following reasons. A state-wide trend analysis of mercury fish tissue concentrations measured over the last 10 – 

15 years indicates only a very slight average rate of decline of about one percent per year. This is not a large 

enough downward trend to justify using only the latest 10 years of data. Also, there have been no significant 

changes in sampling or analytical procedures associated with the fish tissue data that would invalidate the older 

data. It would not be justifiable to remove a waterbody from the 303(d) list simply because the mercury fish 

tissue data for that waterbody were collected more than 10 years ago. With the increased interest in evaluating 

trends in mercury contamination, more lakes and rivers are being resampled. If new data indicates a waterbody is 

no longer impaired, it is removed from the impaired waters list (i.e., “delisted”). No mercury-impaired water has 

been delisted. 

The fish contaminant monitoring program is a multi-agency program that includes the MPCA, the Department of 

Natural Resources (MDNR), the Department of Agriculture, and the Minnesota Department of Health (MDH). 

The primary purpose of the fish contaminant monitoring has been to support MDH’s fish consumption advisory. 

Fish contaminant data are also used by the MPCA to determine where site-specific studies are needed, to help 

identify sources of pollutants, and to look for trends in fish tissue levels. Each year some waterbodies are sampled 

for the first time and some waterbodies are re-sampled. Sample locations are determined by the following: 

MN Statewide Mercury TMDL 27MAR07_final.doc 2
• Where MDNR personnel will be conducting fish population surveys, 

• Waterways where fishing pressure is relatively high, 

• Where previous data are more than ten years old, or 

• Where information is needed for special studies or trend analysis. 

Minnesota has been collecting fish for mercury and polychlorinated biphenyls 

(PCB) tissue analysis since the 1970s. Over the years other bioaccumulative 

pollutants, such as DDT, dioxins and toxaphene have been analyzed in fish 

tissue samples, but only at very limited locations where potential problems were 

suspected. 

The edible portion, which is a skin-on fillet, is prepared in the MPCA fish 

processing lab by DNR personnel. Currently, fish samples are analyzed by the 

Department of Agriculture analytical lab. Since fish bioaccumulate these 

pollutants, concentrations below method detection limits are not usually an 

issue. When they do occur, one half of the method detection limit (less-than value) is used in the assessments. 

The data for each lake or river reach are separated by species and by individual size classes: 5-15, 15-20, 20-25, 

25-30 and 30 + inches. Data collected in the five-year period that includes 

the most recent sampling is averaged. That is, the assessment program 

identifies the most recent data point, then searches back five years for 

additional data from the same waterbody, same species, same size class, and 

averages them. 

MPCA Biomonitoring Unit’s 

Mike Feist holding a stream 

resident 

Fish can be very mobile and difficult to attribute to a discrete portion of a 

lake or river reach; therefore, all fish tissue information from a lake are 

aggregated unless there is evidence to show that fish from certain parts of a 

lake are isolated and may be exposed to different levels of contamination. 

For rivers, fish are collected with nets or electrofishing gear in a range of 

river miles generally not more than five miles apart. Sampled sections of a 

river are associated with river reaches in the USGS hydrologic unit code 

system. However, fish tissue data from one or more sampling station may be 

considered representative of more than just the reach from which they were 

collected. Adjacent river reaches may be listed as well as the reach from 

which the fish were collected based on general information about the home 

range of the species, location of upstream or downstream fish barriers such as 

falls and dams, and significant river tributaries. 

MDNR staff processing fish 

samples for mercury analysis 

2.3 Other State and Federal Regional Mercury TMDLs 

Other mercury TMDLs have been completed prior to completion of this TMDL for mercury-impaired waters in 

Minnesota. This section provides a synopsis of some of those completed mercury TMDLs. 

TMDLs for Lakes Listed for Mercury in Fish Tissue for the Ouachita River Basin, Arkansas – There are 

fish consumption advisories (FCA) throughout the basin (FTN 2003). The Mercury Action Level in Arkansas is 

1.0 mg/kg; the target goal is 0.8 mg/kg, using a 20% margin of safety. 

The TMDL had a two-step approach. The first step estimated the mercury loads from all sources. The second 

step, using largemouth bass tissue mercury concentration, estimated the reduction needed to meet water quality 

MN Statewide Mercury TMDL 27MAR07_final.doc 3
standards (WQS). A linear relationship was assumed between mercury in fish and mercury loading. The fish 

tissue mercury reduction goals were used to determine the load reductions necessary. 

Less than 1% of the existing mercury load is from water point sources. Estimated reductions in mercury loading 

to the basin resulting from the implementation of emission reduction regulations and erosion BMPs were 

calculated. 

Mercury TMDLs for Subsegments Within Mermentau & Vermilion-Teche River Basins, Louisiana – the 

reaches in these basins are listed because of excess mercury in fish tissue (USEPA 2001a). The regional approach 

is justified because atmospheric deposition of mercury is the predominant in these basins. They determined a 

67% reduction in mercury in fish tissue is required to meet WQS. They assumed a linear relationship between 

loading reductions and fish tissue reductions. A ten year implementation schedule was projected. The Binational 

Toxics Strategy sets a national challenge of a 50% reduction of mercury releases by 2006, so that is the interim 

goal. Because of water body mercury recycling and runoff from land surfaces, after deposition reduction goals 

are met, it will be several decades before attainment is met. 

Mercury TMDLs for Little River and Catahoula Lake Watershed, Louisana – these reaches are not meeting 

WQS because of excess mercury in fish tissue (Parsons 2003). An endpoint of 0.5 mg/kg methylmercury in 

edible fish tissue is the target. An estimated 99.5% of current mercury loading is from atmospheric deposition. 

Loadings must be reduced by 32% to meet WQS. Point sources are less than 1% of the load, so are given no 

reduction goal. Since conservative assumptions are made throughout, there is no explicit margin of safety. The 

Binational Toxics Strategy reductions of 50% will easily cover the 32%, according to the TMDL. 

Total Maximum Daily Load [TMDL] for Total Mercury in Fish Tissue Residue in the Middle & Lower 

Savannah River Watershed, Georgia – EPA interpreted Georgia’s WQS and has determined that the applicable 

WQS for total mercury in the ambient water of the Savannah River Basin is 2.8 ng/L (USEPA 2001b). At this 

concentration, or below, fish tissue residue concentrations of mercury will not exceed 0.4 mg/kg, which is 

protective of the general population from consumption of freshwater fish. The TMDL was developed by using 

modeling. Ninety-nine percent of the mercury load is from atmospheric deposition. Based on the modeling, a 

44% reduction goal is required to achieve a water column concentration of 2.8 ng/L. Water point sources will be 

required to create mercury minimization plans. 

3 Applicable Water Quality Standards 

3.1 Mercury Numeric Water Quality Standards 

Mercury numeric water quality standards are based on total (particulate + dissolved) concentrations and thus, total 

mercury measurements in water are used in assessments. Minnesota has two Class 2 water quality standards for 

total mercury: the human health-based statewide standard in Minn. R. ch. 7050 and the wildlife-based standard 

applicable to just the waters of the Lake Superior Basin in Minn. R. ch. 7052. These standards are: 

• 6.9 ng/L. chronic standard, Minn. R. pt. 7050.0222 

• 1.3 ng/L. chronic standard, Minn. R. pt. 7052.0100 

(ng/L = nanogram per liter, or parts per trillion) 

MN Statewide Mercury TMDL 27MAR07_final.doc 4
Minnesota R. ch. 7052 is the Great Lakes Water Quality Initiative (GLI), which focuses on the reduction of 

bioaccumulative toxic chemicals in the Great Lakes ecosystem as a whole.2

 The GLI was mandated by a 1987 

amendment to the Clean Water Act; it was promulgated as a federal rule by EPA in 1995 and adopted in 

Minnesota in 1998. The GLI has been adopted by all eight Great Lakes States, including six states in Region 5. 

The GLI requires wastewater dischargers in the Lake Superior basin to meet a mercury water quality standard of 

1.3 ng/L and implementation of this mercury TMDL does not in any way supercede or conflict with the GLI 

requirements. 

To accurately measure the low levels of mercury in natural waters, the MPCA began using clean sampling 

techniques (EPA Method 1669) and low-level analysis for mercury (EPA Method 1631 or equivalent) in 1996; 

only data collected in this manner are used to assess mercury concentration in water. Mercury levels are assessed 

by comparing concentrations in water to the ambient standards shown above, and by assessing the mercury in fish 

tissue directly (described below). The analysis of mercury in fish tissue does not require as sensitive a method as 

used for water, because of bioaccumulation, and the mercury detection limits for fish tissue have not significantly 

changed since fish tissue analysis began in the mid-1960s. 

In 2001, the USEPA issued a fish tissue residue criterion for methylmercury to protect human health (USEPA 

2001c). The federal methylmercury fish tissue criterion is 0.3 mg/kg. The fish tissue criterion is expected to be 

used by states to establish or update water quality standards. The USEPA chose to express the water quality 

criterion as a fish tissue value rather than a water column value because consumption of fish is the primary route 

of human exposure. MPCA is proposing to adopt this criterion in addition to the 6.9 ng/L mercury water quality 

standard; however, Minnesota’s mercury standard would be 0.2 mg/kg because of higher fish consumption rates 

in the state (See Section 4.3.2 and 4.3.3 for more details). 

3.2 Fish Consumption Advisory 

To ensure the continued good health of people that eat fish in Minnesota, the Minnesota Department of Health 

(MDH) issues guidelines for how often certain fish can be safely eaten, based on the data collected by the fish 

contaminant monitoring program. These guidelines are called the Minnesota Fish Consumption Advisory (FCA) 

(MDH 2004). The MDH, with the help of extensive EPA toxicity and risk assessments for mercury and PCBs, 

establishes the concentrations of contaminants in fish that trigger the various levels of advice – from “unlimited 

consumption” to “do not eat” (Table 1). The FCA is strictly advisory, the goal being to help people that eat fish 

make decisions on which fish to eat and which to avoid. Prior to 2001, the MDH published in booklet form a list 

of all the lakes and rivers that had fish tested and the subsequent consumption advice for those lakes. As of 2001, 

the list of individual water bodies is available on the MDH web site, but it is no longer published as a booklet. 

Instead, the MDH publishes a brochure giving general advice applicable to all fishing lakes (and rivers) in 

Minnesota, regardless of whether the fish from a given lake or river have been tested; exceptions with more 

restrictive consumption advice are listed individually. 

Table 1 Fish Tissue Mercury Concentrations for MDH’s Levels of Consumption Advice 

Mercury Concentration in Fish, ppm 

MFCA for Mercury < 0.05 0.05 - 0.2 >0.2 - 1.0 > 1.0 

Consumption Advice:* Unlimited 1 meal/week 1 meal/month Do not eat 

*Consumption advice for young children and women of child-bearing age. 

 

2

 Minn. R. ch. 7052.0210 imposes restrictions on mixing zones for bioaccumulative chemicals of concern (BCCs). 

Allowance for mixing zones for BCCs are scheduled to end in 2007 (See Section 10.3). 

MN Statewide Mercury TMDL 27MAR07_final.doc 5
The MDH fish consumption advice and the MPCA impairment determinations are based on the same EPAderived reference dose. Reference dose, expressed in units of daily dose, is an estimate of the daily exposure to 

human populations, including sensitive sub-populations, that is likely to be without appreciable risk of deleterious 

effects over a lifetime. A good summary of the toxicity assessment and derivation of the reference dose for 

mercury is included in the most recent USEPA mercury criterion document (EPA 2001c). 

While the FCA is not mandatory, the 303(d) list of impaired waters is mandatory, listing waterbodies that do not 

meet legally enforceable water quality standards, and requiring Total Maximum Daily Load studies of those 

impaired waters. 

Contaminants in fish can be a threat to wildlife consumers of fish and other aquatic organisms as well as humans. 

Minnesota does not have a program to analyze whole fish samples for the purpose of assessing risks to wildlife; 

however, the water quality standard for the Lake Superior basin (1.3 ng Hg/L) is based on wildlife toxicity of 

mercury via fish consumption. 

3.3 Basis for Assessment of Fish Contaminants – Narrative Standards 

3.3.1 Minnesota Rule Chapter 7050 

The basis for assessing the contaminants in fish tissue is the narrative water quality standards and assessment 

factors in Minn. R. pt. 7050.0150, subp. 7 which is quoted below: 

Subp. 7. Impairment of waters relating to fish for human consumption. In evaluating whether the narrative 

standards in subpart 3, which prevent harmful pesticide or other residues in aquatic flora or fauna, are being met, 

the commissioner will use the residue levels in fish muscle tissue established by the Minnesota Department of Health 

to identify surface waters supporting fish for which the Minnesota Department of Health recommends a reduced 

frequency of fish consumption for the protection of public health. A water body will be considered impaired when 

the recommended consumption frequency is less than one meal per week, such as one meal per month, for any 

member of the population. That is, a water body will not be considered impaired if the recommended consumption 

frequency is one meal per week, or any less restrictive recommendation such as two meals per week, for all members 

of the population. The impaired condition must be supported with measured data on the contaminant levels in the 

indigenous fish. 

3.3.2 Selection of Single Fish Meal-Per-Week Impairment Threshold 

The EPA has promulgated a methylmercury criterion for fish tissue because the consumption of fish is the most 

important route of exposure of mercury to humans. The two aspects of a criterion are toxicity and exposure. The 

MPCA relies on the assessments of mercury toxicity to humans by the experts within EPA and MDH. Exposure 

varies with how often people eat fish and with the mercury concentrations in the fish they eat. The EPA assumes 

people eat 17.5 grams per day for purposes of calculating their human health-based aquatic life criteria (EPA 

2000c). This generic assumption applies to everybody in the U.S. The MPCA uses a higher consumption rate for 

determining exposure because of the prevalence and importance of sport fishing in Minnesota. Minnesota human 

health-based water quality standards are calculated assuming people eat 30 grams of fish per day, which is the 80th

percentile fish consumption rate of sport-caught fish for the angling population, based on several surveys of the 

fish eating habits of upper Midwest anglers (not the population as a whole) (MPCA 2000). 

The surveys from which the 30 g/d value was derived indicate that less than 20 percent of anglers and less than 95 

percent of the whole population in the upper Midwest eat more sport-caught fish than one meal-per-week 

averaged over a lifetime (MPCA 2000). A more recent survey of fish consumption habits of people living in 

Minnesota and North Dakota suggests that 30 g/d may be more protective than these earlier surveys indicate 

(EERC 2001). The 95th percentile consumption rates of sport-caught fish for all Minnesotans with fishing 

licenses reported in the EERC survey is 30.4 g/d (32.1 g/d in a lognormal distribution). 

MN Statewide Mercury TMDL 27MAR07_final.doc 6
Thirty grams per day equals about a half-pound meal per week (0.463 pounds/week). The single fish meal-perweek consumption rate (or 30 g/d) is the basis for all Minnesota human health-based water quality standards in 

both Minn. R. chs. 7050 and 7052. Therefore, “fish consumption” use is supported if it is safe to eat one fish 

meal per week (over a life time), consistent with the assumption inherent in the numeric water quality standards. 

In other words, MDH’s advice to limit consumption to “no more than one meal-per-week” (or advise that allows 

more consumption) is not considered an exceedance of the mercury water quality standards, and waterbodies with 

such advice are not listed as impaired. Advice to limit consumption to less than one meal per week, such as one 

meal per month, for any member of the population, indicates impairment. 

3.3.3 Fish Tissue Criterion for Mercury 

Relevant to the assessment of mercury in fish is the issuance by EPA of a revised human health-based water 

quality criterion for methylmercury (EPA 2001c). This new criterion is unique among all EPA (Clean Water Act 

section 304(a)) criteria in that the medium for the acceptable mercury concentration is fish tissue rather than 

water. A fish tissue criterion for mercury is logical because it is fish that are the main source of methylmercury 

exposure to both humans and wildlife. Also, a tissue-based criterion eliminates the need for a bioaccumulation 

factor in the criterion calculation, which can be a significant source of uncertainty. The bioaccumulation factor is 

the ratio of fish concentration to water concentration. The new EPA criterion is 0.3 mg/kg (ppm) methylmercury 

in fish muscle tissue. Since nearly 100 percent of the mercury in fish muscle is methylmercury, it is essentially a 

total mercury criterion. 

In the determination of the 0.3 ppm criterion, EPA assumes people eat 17.5 grams of fish per day, as mentioned 

above. If the EPA criterion is re-calculated assuming people eat 30 g/day, the criterion becomes 0.17 ppm. This 

EPA criterion and the MFCA are both based on the same EPA-derived reference dose of 0.1 μg/kg/day. The 

difference between the MDH value of 0.2 ppm and the re-calculated EPA criterion of 0.17 ppm, both of which 

assume a single half pound meal of fish per week, has to do with how the consumption of marine fish is taken into 

account. The MFCA is advice about eating fish from any source, sport-caught, store-bought, marine or 

freshwater. The EPA aquatic life criteria (applicable in Minnesota) apply only to freshwater habitats. But, in the 

calculation of freshwater criteria, EPA assumes people eat a certain amount of marine fish in addition to the 17.5 

g/d of freshwater fish. As a result, the freshwater criterion is lowered to allow for this “outside” source of 

mercury (this is standard procedure in EPA criteria and MPCA standard calculations). Thus, the re-calculated 

mercury criterion ends up at 0.17 rather than 0.2 ppm. The MPCA believes that the use of 0.2 ppm, rather than 

0.17 ppm as the basis for impairment decisions is appropriate for the following reasons: 

• EPA rounded the reference dose of 0.1 μg/kg/day to one significant figure; thus, 0.17 and 0.2 ppm could 

be considered essentially the same number,

• The use by MPCA of the more protective fish consumption amount (30 g/d), 

• The use of safety factors in the criterion calculation (again, standard procedure), 

• Uncertainties inherent in criteria development, and 

• The importance of maintaining consistency in the MPCA/MDH approaches. 

4 Minnesota’s Regional Approach 

4.1 Land Cover and Water Quality 

The primary source of mercury to the state’s water bodies is atmospheric deposition, which is approximately 

uniform across the state (See Section 5.1). Mercury concentrations in fish, however, vary widely on both large 

and small scales. A major factor causing this spatial variability in fish mercury levels is land cover and use, 

MN Statewide Mercury TMDL 27MAR07_final.doc 7
which affects watershed transport of mercury, background water chemistry, and nutrients. The water quality 

differences, influenced by the nutrient loading, in turn influence the bioavailability of mercury. Wetlands – an 

important land cover in Minnesota – are important sites of mercury methylation, because sulfate-reducing bacteria 

(SRB) are the primary methylators and they thrive in wetlands. Additional sulfate to a wetland can stimulate SRB 

activity, leading to increased mercury methylation (See Section 5.4). Methylmercury associated with dissolved 

organic carbon released from wetlands is conveyed to surface waters (Driscoll et al. 1995). Consequently, 

wetland density is correlated with mercury concentrations in water and fish (e.g. Greenfield et al. 2001, Knights et 

al. 2005). Compared to wetland and forested lands, cultivated lands are typically sources of high suspended 

solids because of soil erosion. Research in Minnesota has shown mercury is associated with the high suspended 

solids loads (Balogh et al 1997, Balogh et al. 1998), although most of the mercury associated with the solids has 

low bioavailability, because only a small fraction is methylmercury. 

A concise literature review of the relationship between lake trophic status and fish mercury concentration was 

provided by Fink et al. (2001). Studying Swedish lakes, Johnels et al. (1967) observed that high fish mercury 

levels were less likely in nutrient-enriched or eutrophic lakes than in unenriched or oligotrophic lakes. The same 

observation was made by D’Itri et al. (1971) and Hakanson (1974); and was attributed to the buffering or dilution 

effect caused by an increase in suspended solids of biological origin. Several processes may contribute to this 

“biodilution” effect: (1) increased biomass for sorbing the mercury, (2) increased settling rate of biomass, which 

removes sorbed mercury from the water column, and (3) increased growth rate of fish, resulting in larger size for 

a given age class (Norstrom et al., 1976). The biodilution effect has been demonstrated in laboratory microcosms 

(Pickhardt et al. 2002) and in empirical field studies (Chen and Folt 2005) 

4.2 Ecoregions 

Regional patterns in lake water quality have been documented for ecoregions in Minnesota (Heiskary, Wilson, 

and Larsen 1987). The State is divided into seven Level III ecoregions (Omernik and Gallant 1988): Northern 

Lakes and Forest, Northern Minnesota Wetlands, Red River Valley, North Central Hardwood Forests, Northern 

Glaciated Plains, Western Corn Belt Plains, and Driftless Area. The principle that land use influences water 

quality has been put to good use in the development of nutrient criteria for the state. Phosphorus criteria have 

been proposed based on ecoregions (Heiskary and Walker 1988). A similar approach is proposed for this TMDL 

to assess mercury loading. 

For the purposes of the Minnesota mercury TMDL, the Northern Lakes and Forest ecoregion and the Northern 

Minnesota Wetlands ecoregion are combined to form the Northeast (NE) region; the other ecoregions are 

combined to form the Southwest (SW) region (Table 2; Figure 2). Differences between the NE and SW regions 

are described below. Impaired reaches along the NE/SW boundary were examined and some river reaches were 

reassigned to maintain a TMDL connection with downstream reaches. A Twin Cities Metro region was 

considered, based on the dominance of urban land use (i.e., impervious area); however, the fish tissue mercury 

concentrations for the Metro region were the same as the SW; therefore, the Metro region was combined with the 

SW region (See Section 4.4). 

NE and SW regions are distinct in terms of land cover/use and in water quality (Table 2). The NE region is 

dominated by wetlands and has less than ten percent cultivated land; the SW region, overall, has less than ten 

percent wetlands and is dominated by cultivated land. The NE region has an abundance of dystrophic and 

oligotrophic lakes; the latter is evident by the very low total phosphorus and chlorophyll a concentrations (Table 

2). In contrast, the SW region has chlorophyll concentrations that are 2 to 10 times higher than the NE region 

levels. The regional differences in mercury transport and transformation processes result in significantly different 

average fish tissue mercury concentrations (see Section 4.4). 

MN Statewide Mercury TMDL 27MAR07_final.doc 8
Table 2 Regional Differences in Land Cover and Water Quality 

Region 

Ecoregion Wetlands 

(%) 

Cultivated 

(%) 

Hay/ 

Pasture 

(%) 

Lake TP 

(μg/L) 

Stream TP 

(μg/L) 

Lake 

Chl a

(μg/L) 

Stream 

Chl a 

(μg/L) 

NMW 58.9 8.3 4.6 14 – 27 40 – 90 2-10 3.2 NE NLF 26.9 3.6 6.5 14 – 27 20 – 50 2-10 2.1 

NCHF 14.9 35.0 23.4 23 – 50 60 – 150 5 – 22 15.8 

RRV 7.3 78.8 6.6 23 – 50 110 – 300 5 – 22 22.1 

NGP 4.6 73.5 16.5 130 – 250 90 – 250 30 – 55 27.1 

DA 4.5 23.8 27.1 N/A 60 – 150 N/A N/A 

SW 

WCBP 2.9 76.8 12.2 65 – 150 160 – 330 30 – 80 23.6 

NMW: Northern Minnesota Wetlands RRV: Red River Valley 

NLF: Northern Lakes and Forests NGP: Northern Glaciated Plains 

NCHF: North Central Hardwoods Forests DA: Driftless Area 

WCBP: Western Corn Belt Plains 

Land cover data from 1992 (USGS, 1999. Minnesota Land Cover Data Set) 

Total phosphorus (TP) and chlorophyll a (Chl a) ranges are typical summer lake water quality conditions and typical 

annual stream water quality conditions for minimally impacted waters (MPCA. 2003. Comparison of typical Minnesota 

water quality conditions. http://www.pca.state.mn.us/publications/wq-s1-02.pdf ). Lake data were collected 1985-1988 

(Heiskary and Wilson 1989) and stream data were collected 1990-1992 (McCollor and Heiskary 1993). 

4.3 Baseline Year: 1990 

The baseline year for the Minnesota mercury TMDL is 1990, because (1) the most recent measurement of total 

(wet and dry) mercury deposition in Minnesota is based on lake sediment cores collected around 1990, (2) it is a 

well-established baseline for mercury emissions inventories and, most importantly (3) it represents the end of a 

period when mercury emissions and fish concentrations were most likely in a steady state. Minnesota’s Mercury 

Emissions Inventory (MPCA 2005; see Figure 13 on page 28) and goals established in Minnesota’s Mercury 

Reduction Law are based on the 1990 baseline. The USEPA has also used 1990 as the baseline for presenting 

U.S. mercury emissions (see Figure 12 on page 27). The Great Lakes Binational Toxics Strategy 

(http://www.epa.gov/glnpo/p2/bns.html) and the Lake Superior Lakewide Management Plan 

(http//www.epa.gov/glnpo/lakesuperior/chapter3.html) use 1990 for assessing reductions in mercury releases. 

This regional mercury TMDL relies on mercury deposition being in a dynamic equilibrium, or steady state, with 

mercury in fish. No one knows how long it takes for fish mercury levels to reflect change in mercury use and 

emissions, but the lag time is most likely more than 5 years, because of lags in mercury disposal, deposition, 

methylation, and fish growth. There were rapid changes in mercury use and emissions in the 1990s, as mercury 

use was eliminated in products (paint, golf course fungicides, alkaline batteries) and incinerator emissions were 

progressively controlled (see Section 5). As a result, one would not expect fish to be in steady state with 

contemporaneous mercury emissions after 1990. Therefore, this TMDL establishes the relationship between 

mercury emissions and fish contamination using data from 1990 or earlier, when conditions had been relatively 

stable for 10 years (see Figure 11 on page 27). 

The best estimate of total mercury deposition is based on sediment cores from Minnesota lakes (Swain et al. 

1992). Total mercury deposition includes wet and dry deposition. Wet deposition is measured through the 

Mercury Deposition Network (beginning in 1996) at five locations within or very close to Minnesota, as well as 

other places throughout the country (http://nadp.sws.uiuc.edu/mdn/). Dry deposition cannot be measured directly, 

like wet deposition. Therefore, it is not possible to measure total mercury deposition directly. The best measure 

of total deposition generally accepted among scientists is based on sediment core analysis. Based on sediment 

cores collected in Minnesota lakes, the best estimate for total mercury deposition around 1990 is 12.5 g km-2 yr-1. 

This total mercury deposition value cannot be correlated with wet deposition measurements, because wet 

MN Statewide Mercury TMDL 27MAR07_final.doc 9
Figure 2 TMDL Regional Areas and Mercury-Impaired Waters 

MN Statewide Mercury TMDL 27MAR07_final.doc 10
deposition monitoring began later. Therefore, we cannot use the measured wet deposition to derive a reasonable 

estimate of total mercury deposition for 2000 or 2005. Sediment cores have a time resolution of about ten years. 

Because of the difficulty measuring total mercury deposition, mercury emissions goals are more practical for the 

TMDL. 

4.4 Target Levels of Fish Mercury Concentration 

4.4.1 Standard Size Predator Fish 

The fish tissue mercury concentration of 0.2 ppm is the mercury TMDL target level. This section describes how 

the target level is used to derive a mercury reduction factor for each region. 

The Minnesota Fish Consumption Advisory (FCA) divides meal advise into five size classes (5-15, 15-20, 20-25, 

25-30, 30+ inches); the 0.2 ppm fish tissue mercury concentration is compared to the average for a particular size 

class of a specific species within a specific water body. For example, a river reach would be considered impaired 

if the average mercury concentration for the 20-25 inch size class carp was above 0.2 ppm. In the SW region, 

there are 24 species that had a size class exceed the 0.2 ppm threshold and 32 species in the NE region (Figure 3). 

Most of these species are only representative of one or two waterbodies. It is not practical to assign a target value 

for every species for the purposes of this TMDL. Rather, our choice is to use top predators – northern pike and 

walleye– as the target species, because they have the highest mercury concentrations and are the most common 

species representing impaired waters. If the top predators meet the water quality standard, then other species and 

the water column will too. 

For temporal and spatial comparisons of mercury concentrations in the top predator fish, we calculate a mercury 

concentration for a standard length fish. When fish are captured for mercury analysis, the number and size of fish 

will vary among lakes and among trips to the same lake. Because mercury concentration increases with fish age 

and fish increase in length with age, comparing the average mercury concentrations among lakes would not 

account for this relationship to the size of the fish. A sample set from one year could have a higher average 

mercury concentration than another year because the average fish size was larger the first year; therefore, average 

concentrations would represent a change in average fish size rather than a real change in mercury concentration. 

To account for this size-dependency of mercury concentrations, the mercury concentration is compared for the 

same size fish, which we refer to as the standard size or standard length fish. One cannot simply select the 

standard length fish from the collection of fish each time because lengths of collected fish vary from year to year 

(and lake to lake). The mercury concentration in the standard length fish is calculated for each collection using a 

linear regression statistical procedure, which gives a mercury concentration per length of fish. The linear 

regression is done mathematically. It is illustrated by plotting mercury concentration (on the vertical axis) versus 

the fish length (on the horizontal axis) and drawing a best fit line through the points. The line represents the best 

estimate of mercury concentration per fish length and can be used to predict mercury concentration for any fish 

length under the line. In other words, this process allows one to predict the mercury concentration for a predetermined size of fish based on the available fish data. A collection may have as few as three fish or up to fifty 

fish, which are used to predict the standard length fish mercury concentration. That single value for the standard 

length fish can then represent the mercury concentration for the fish from that collection. If the standard length 

fish mercury concentration decreases between sample collections (and the relationship between age and length of 

fish does not change), we know that mercury concentrations in that fish species from that water body has 

decreased and has not changed simply because the collected fish are smaller. 

MN Statewide Mercury TMDL 27MAR07_final.doc 11
MN Statewide Mercury TMDL 27MAR07_final.doc 

Hg (=>0.2) NE Region

Bigmouth Buf Black Bullhe Black Crappi Bluegill Sun

SPECIES

Bow

Brown Bullhe Brown Trout Burbot Carp Chinook 

Lake Trout Lake Whitefi Largemouth B Muskellunge Northe

Redhorse Suc Rock Bass Sauger Shorthead Re Silver R

Smallmouth B Snapping Tur Splake

5-1515-2020-2525-3030 +

SIZECLASS

Sucker

5-1515-2020-2525-3030 +

SIZECLASS

Wal

5-1515-2020-2

SIZEC

Yellow Bullh

5-1515-2020-2525-3030 +

SIZECLASS

Yellow Perch

5-1515-2020-2525-3030 +

SIZECLASS

012345

H

G

Hg (=>0.2) SW Region

Bass Black Bullhe Black Crappi Bluegill Sun

SPECIES

Carp Channel Catf

0.00.51.01.52.0

H

G

Cisco Crappie Freshwater D Largemouth B Muskellunge Northern Pik

0.00.51.01.52.0

H

G

Redhorse Suc Rock Bass Shorthead Re Silver Redho Smallmouth B Snapping Tur

0.00.51.01.52.0

H

G

Walleye

5-1515-2020-2525-3030 +

SIZECLASS

White Bass

5-1515-2020-2525-3030 +

SIZECLASS

White Crappi

5-1515-2020-2525-3030 +

SIZECLASS

White Sucker

5-1515-2020-2525-3030 +

SIZECLASS

Yellow Bullh

5-1515-2020-2525-3030 +

SIZECLASS

Yellow Perch

5-1515-2020-2525-3030 +

SIZECLASS

0.00.51.01.52.0

H

G

Figure 3 Average Fish Tissue Mercury Concentration Greater Than 0.2 ppm by Species and Size Class 
MN State

NP55 is 21.65 in (~22 in) and WE40 is 15.75 in (~16 in); therefore, they are in the 20-25 inch and 15-20 

inch size classes used by the FCA. Size class distributions of northern pike and walleye within the two 

regions indicate the mode (most common or highest frequency) size class for northern pike (NP) in both 

regions is 20-25 inches and the mode size class for walleye (WE) in both regions is 15-20 inches (Figure 

4Error! Reference source not found.). Therefore, the standard lengths provide a good correspondence 

to the most common size class for northern pike and walleye throughout Minnesota. 

The 55 cm northern pike (NP55) has represented the standard length fish in many scientific mercury 

studies. Sweden has used the 1-kilogram northern pike—which is approximately equivalent to a length of 

55 cm—for mercury studies since the 1960s (Johnels et al. 1967). That standard fish length was used by 

Sorensen et al. (1990) in their study of mercury in northern Minnesota lakes. They compared a range of 

walleye and northern pike fish lengths and found that a 39 cm walleye had the best correlation to a 55 cm 

northern pike. The MPCA has continued to use the NP55 and a 40 cm walleye (WE40) as the standard 

length fish to compare among lakes and rivers. 

An important aspect of the standard size fish mercury concentration is that it is based on a set of data from 

a water body, not a single data point; therefore, unlike a single data point, a measure of uncertainty (such 

as a confidence interval) can be assigned to the value. The measure of uncertainty will vary with the 

number of data points available and the variability of the data. For future assessments, the standard size 

fish mercury concentrations can be evaluated to see if there has been a statistically significant change in 

fish tissue mercury concentrations. 

wide Mercury TMDL 27MAR07_final.doc 13

NE,NP

4.4.2 Applying the Target Level to the 90th Percentile Fish Concentration 

To achieve water quality standards and protect water bodies from impairment, an appropriate statistic 

must be selected to meet the target level of 0.2 ppm. Rather than using a measure of central tendency, 

such as the mean or median, the 90th percentile (90%) was selected to provide greater protection. The 90th

percentile of samples from a given waterbody has been used as assessment guidance by the USEPA (i.e., 

Figure 4 Size Class Distributions by Region (NE, SW) and Species (NP, WE) 

Count Count 100

200

300

100

200

300

400

500

600

5-15 15-20 20-25 25-30 30 +

SIZECLASS

0

0

0.0

0.1

0.2

0.3

0.4

Proportion per Bar

NE,WE

5-15 15-20 20-25 25-30 30 +

SIZECLASS

0

100

200

300

400

500

Count

0.0

0.1

0.2

0.3

0.4

Proportion per Bar

SW,NP

5-15 15-20 20-25 25-30 30 +

SIZECLASS

0.0

0.1

0.2

0.3

0.4

Proportion per Bar

100

150

200

250

50

SW,WE

5-15 15-20 20-25 25-30 30 +

SIZECLASS

0

Count

0.0

0.1

0.2

0.3

0.4

Proportion per Bar
no more than 10% of the samples can exceed the standard). Achieving the target level for the 90th

percentile of standard size predator fish ensures that 100% of the smaller predator fish and fish at lower 

trophic levels will meet the target level. 

Selecting a higher percentile is not necessary or reasonable. As fish mercury levels are reduced and the 

90th percentile approaches 0.2 ppm, the concentration difference between the 90th and the 99th is likely to 

be very small. Futhermore, the 90th percentile allows for outliers that may have unique circumstances. 

The outliers can be addressed individually as part of the adaptive watershed management approach to 

TMDL implementation. 

The median (50%) and 90th percentile (90%) mercury concentrations for NP and WE in the two regions 

are shown in Table 3, based on the period of record (1970-2002). Median mercury concentrations in the 

20-25 in size class of NP are similar to the median for the standard length NP for both regions; and the 

similarity also holds for the 90th percentiles. For WE, the match between mode size class (15-20 in) and 

standard fish length is not as good as in NP. The WE mercury concentrations are lower, which is not 

surprising since the standard length WE (16 in.) is near the small end of the 15-20 inch size class and 

mercury concentrations generally increase with fish length; nonetheless, there is less than a 20% 

difference between the median and 90th percentile statistics. 

Table 3 Mercury Concentrations for Northern Pike (NP) and Walleye (WE) 

Collected from 1970 to 2002 

Species: NP WE 

Region 

Size Class 

(in): 20-25 

Std 22 

(NP55) 15-20 

Std16 

(WE40) 

N 433 712 375 584 

NE Median 0.310 0.320 0.318 0.268 

90% 0.645 0.641 0.677 0.631 

N 207 265 174 220 

SW Median 0.190 0.187 0.212 0.185 

90% 0.425 0.368 0.470 0.390 

To establish the target level for the baseline year, data from 1988 through 1992 were used to provide a 

five-year dataset centered around 1990. Five years of fish tissue data provides some accounting for year 

to year variability in weather, sampling locations, and natural variability in fish populations. The spatial 

distribution of the fish tissue data reflects distribution of lakes throughout the state; most of the lakes are 

in the NLF and CHF ecoregions (Figure 5). Many of the lakes had both walleye and northern pike 

collected and were usually closely matched in fish mercury concentration. The highest mercury 

concentrations are clearly shown in the northeastern area of the NE region, which includes the Voyageurs 

National Park and Boundary Waters Wilderness Canoe Area. 

Not all mercury impaired waters are included in this mercury TMDL. To ensure that water quality 

standards are met when the TMDL reduction goal is achieved, only lakes and streams with fish size class 

mercury concentrations less than 0.572 mg/kg are included (see Appendix A). In other words, only 

impaired waters with fish size class mercury concentrations that require a reduction of 65% or less are 

included in this mercury TMDL. MPCA will continue to monitor and assess the other mercury impaired 

waters, and where feasible, develop waterbody-specific mercury TMDLs. 

MN Statewide Mercury TMDL 27MAR07_final.doc 14
Figure 5 Standard size northern pike and walleye distribution 

MN Statewide Mercury TMDL 27MAR07_final.doc 15
NP

NE

WE

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Fra

ctio

n

of D

ata

SW

0.0 0.1 1.0

HGPPM

0.0 0.1 1.0

HGPPM

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Fra

ctio

n

of D

ata

Figure 6 Mercury Distributions by Species and Region for 1988-1992 

Figure 6 shows the distribution of mercury concentrations for each standard length species, within each 

region; the vertical dashed line indicates the 0.2 ppm Hg concentration. Our general goal is to shift the 

distribution to the left, but for the purpose of assigning a goal or target level, a single statistic is necessary. 

The medians and 90th percentiles for 1988-1992 are similar to the whole period of record—1970-2002 

(Table 4). The median mercury concentrations in the SW region are actually close to the 0.2 ppm target 

concentration. Applying the target concentration to the median would clearly not be sufficient to achieve 

water quality standards in most of the impaired waters within that region. 

Table 4 Mercury Concentrations Standard Size Northern Pike and Walleye for 1988-1992 

Region Statistic NP WE 

N 138 156

NE Median 0.293 0.262

90% 0.545 0.572

N 66 74

SW Median 0.203 0.218

90% 0.373 0.405

The 90th percentile mercury concentration provides greater protection than the median and, therefore, was 

selected as the basis for establishing reduction factors (Table 5). The reduction factor (RF) is the percent 

reduction needed to achieve 0.2 ppm Hg for the 90th percentile of the standard length fish mercury 

concentration. Mercury concentrations in standard length walleye (WE4090) were higher than standard 

length northern pike (NP5590) in both regions; therefore, the walleye require a greater reduction factor 

MN Statewide Mercury TMDL 27MAR07_final.doc 16
than the northern pike, and achieving the target level for walleye provides a greater level of protection. 

Consequently, we selected the more protective reduction factors of 51% for the SW region and 

65% for the NE region. 

Table 5 Reduction Factors Based on the Baseline Year: 1990 

Region Target Species 

Hg* 

(mg/kg) RF** 

NP5590 0.545 63% NE 

WE4090 0.572 65% 

NP5590 0.373 46% SW 

WE4090 0.405 51% 

* 90th percentile for fish mercury data from 1988-1992 

** RF: Reduction Factor = (NP5590 - 0.2)/NP5590 or 

 = (WE4090 - 0.2)/WE4090

As mentioned in Section 3, a third, Metro region, defined by the seven county Twin Cities metro area, 

was considered. The Metro region was separated from the SW region because presumed greater 

predominance of impervious land cover in the metro region, and potentially higher mercury loading via 

stormwater. As shown in Figure 7, the SW and Metro had identical 90th percentiles for standard size 

northern pike (NP), and the walleye (WE) differed by only 0.028 mg/kg (relative percent difference: 7%). 

The difference between Reduction Factors for SW and Metro WE was only three percent. Given that the 

Metro region would otherwise be included in SW region and the similarity of the 90th percentiles would 

result in the same reduction factors, the data from the Metro region were combined with the SW for the 

final mercury TMDL calculations. 

95th %'tle

95th %'tle

90th %'tle

90th %'tle

75th %'tle

75th %'tle

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Fish Hg (ppm-ww)

95th %'tle 0.657 0.657 0.390 0.458 0.427 0.508

90th %'tle 0.545 0.572 0.372 0.372 0.391 0.419

75th %'tle 0.402 0.422 0.301 0.303 0.313 0.319

NE/NP NE/WE SW/NP METRO/NP SW/WE METRO/WE

error bars ± 5%

Figure 7 Upper percentiles for northern pike (NP and walleye (WE) 

in the NE, SW, and Metro Regions 

MN Statewide Mercury TMDL 27MAR07_final.doc 17
4.4.3 Achieving Water Quality Criteria for Mercury 

Water column impairments for total mercury are expected to meet water quality standards when the fish 

tissue target is reached. Minnesota’s water column chronic standards for total mercury are 6.9 ng/L 

statewide and 1.3 ng/L in the Lake Superior basin. The fish tissue target concentration is 0.2 mg/kg. The 

0.2 mg/kg fish tissue target can be divided by a representative bioaccumulation factor (BAF) to get a 

comparable water column mercury concentration. Our best set of BAFs for fish mercury concentrations 

and total mercury concentrations comes from 14 lakes representing three geographic areas of Minnesota 

(Table 6). The lakes representing the agricultural area (“Ag”) and the Twin Cities metropolitan area 

(“Metro”) are in the SW region; lakes representing the forested area (“Forest”) are in the NE region. 

Water column concentrations are based on five samples collected in 2000-2001, and standard size 

northern pike and walleye mercury concentrations are from 1999-2001. Table 1 shows the geometric 

mean for the 14 BAFs is 388,424 L/kg. 

Using the geometric mean BAF, the calculated water concentration for a 0.2 mg/kg fish mercury 

concentration is 0.52 ng/L; well below the statewide and Lake Superior basin water quality standards. 

The fifth percentile of the 14 lake BAFs gives a comparable water column mercury concentration of 1.3 

ng/L. Therefore, these results provide reasonable assurance that the water column mercury concentration 

will be met when the fish tissue target is reached. 

Table 6 Bioaccumulation factors for 14 representative lakes in Minnesota 

REGION DOWID WATERWAY SP-YR N 

NP55

(mg/kg)

Water 

(median, 

ng/L) 

BAF 

(NP55/Water)

Ag 07-0053 Duck NP-00 7 0.034 1.057 32,587

Ag 47-0082 Dunns NP-99 5 0.256 1.180 216,875

Forest 38-0231 Tettegouche NP-00 24 0.258 1.090 236,676

Ag 41-0089 Shaokatan WE-00 22 0.203 0.753 269,495

Metro 62-0056 Owasso NP-01 24 0.148 0.423 351,046

Forest 38-0242 Wolf WE-99 14 0.184 0.523 352,242

Forest 38-0068 Windy NP-99 10 0.708 1.753 404,178

Metro 27-0016 Harriet WE-00 19 0.231 0.488 473,875

Metro 27-0031 Calhoun WE-00 24 0.262 0.495 528,474

Metro 27-0039 Cedar NP-00 6 0.356 0.599 594,455

Ag 47-0088 Richardson NP-99 15 0.305 0.496 614,931

Forest 29-0015 Williams NP-99 24 0.264 0.425 622,780

Metro 27-0137 Christmas NP-01 26 0.223 0.229 971,214

Forest 29-0043 Shingobee NP-00 7 0.342 0.240 1,426,490

Min: 0.034 0.229 32,587

Max: 0.708 1.753 1,426,490

Geomean: 0.270 0.696 388,424

5 Source Assessment and Trends 

5.1 Sources of Mercury in Minnesota Fish 

Pollutant sources to water are divided into point sources and nonpoint sources. Point sources include any 

discharge to a water body via a pipe or channel, including publicly owned wastewater treatment plants, 

industrial waste dischargers, and municipal stormwater discharge. Nonpoint sources, as the name 

implies, include all other sources, such as the diffuse sources of runoff and air deposition. 

In the late 1960s, when mercury contamination of fish was first discovered in Sweden, Canada, 

Minnesota and other places in the United States, the source of mercury was unknown. It was unclear 

whether the mercury was derived from local geology or delivered by the atmosphere. Scientists knew 

MN Statewide Mercury TMDL 27MAR07_final.doc 18
that mercury must be methylated before it can be accumulated by fish, but they did not know where 

methylation occurred, whether it was in soil, water, sediment or in the gut of the fish itself. Nevertheless, 

without mercury there could be no mercury methylation. In the early 1970s, steps were taken to eliminate 

the obvious sources of mercury to rivers and lakes. These steps included greatly reducing activities that 

could cause mercury to be discharged to waterways, such as the use of mercury fungicides in paper 

making and by mercury cell chlor-alkali plants. But because fish were contaminated in remote lakes that 

never received any industrial discharge, some scientists suspected that the atmosphere was delivering 

significant quantities of mercury. Significant geological sources of mercury are localized in cinnabar 

deposits in such places as the coastal range of California and in Almaden, Spain. The geology of most of 

the United States, including Minnesota, does not contain concentrated sources of mercury. 

Much has been learned about environmental mercury in the decades since. By the early 1990s, it was 

clear that the atmosphere is the main source of mercury to most surface waters. By 1994, an expert panel 

(Expert Panel 1994) was able to conclude that anthropogenic activities accounted for 50 to 75% of 

mercury emissions to the atmosphere, and hence 50 to 75% of mercury 

deposition to aquatic systems. A more recent study in Minnesota 

(Engstrom and Swain 1997) indicated anthropogenic sources 

contribute 70% of the mercury deposition to the state. 

The 70% proportion was calculated by the relative change in mercury 

accumulation in seven rural lakes, as presented in Swain et al. (1992). 

According to those calculations, atmospheric mercury deposition in the 

rural upper Midwest increased from 3.7 g km-2 yr-1) in 1850 to 12.5 g 

km-2 yr-1 in 1990. If 3.7 was the natural deposition rate, then natural 

sources contributed 30% of total deposition in 1990, leaving 70% as 

anthropogenic. Between 10 and 15 sediment cores from each of seven 

lakes were needed to account for the total mercury deposition. This 

type of data collection has not been performed on a national scale. 

Our ability to understand and model the atmospheric transport and 

deposition of mercury is hampered by the various chemical forms that 

mercury can assume. Mercury can be emitted from anthropogenic 

(human) sources as either elemental or divalent forms, and most likely can interconvert in the atmosphere 

through chemical reactions. Essentially all mercury emitted to the atmosphere will eventually deposit on 

the Earth’s surface. Because of uncertainty about atmospheric chemistry, predicting where or when will 

deposit is difficult. The fundamental chemical uncertainty is the conversion from elemental mercury 

vapor to divalent mercury. Elemental mercury vapor is relatively inert, and therefore may remain in the 

atmosphere up to one year, allowing long-distance dispersal before deposition to terrestrial or aquatic 

systems. Divalent mercury, on the other hand, is much more readily removed from the atmosphere in rain 

(“wet” deposition) because it is water soluble and tends to stick to surfaces, including those of airborne 

dust, vegetation, and even dew (“dry” deposition). Scientists use complex computer models to simulate 

the atmospheric processes and deposition. The models are continually refined as new scientific 

understanding becomes available, but because much remains unknown, there is considerable uncertainty 

in the predictions. 

Ed Swain and Dan Engstrom 

collecting a sediment core 

After mercury deposits on to the Earth’s surface only a small proportion of mercury becomes geologically 

immobilized through burial in the sediments of lakes, oceans or river deltas. Mercury deposited to soils is 

held for a geologically short time (tens or hundreds of years), from which it can be leached, eroded or 

volatilized back to the atmosphere. A small proportion of the deposited mercury makes its way to 

environments where it may be methylated (wetlands, lakes and rivers). 

Worldwide trends in mercury emissions and deposition must be in approximate balance, because any 

emitted mercury must come down somewhere, sometime. Gaseous elemental mercury has an average 

MN Statewide Mercury TMDL 27MAR07_final.doc 19
atmospheric residence time of up to one year, therefore, time lags in deposition should not be significant 

when viewed on a multi-year basis. Volatilization from soils of atmospherically deposited mercury may 

produce a significant lag, or smoothing, of deposition compared to primary anthropogenic emissions, but 

this effect has not been adequately studied and quantified. Erosion or leaching of mercury to aquatic 

systems from terrestrial soils is known to be significant in some watersheds (e.g., Balogh et al. 1997, 

Balogh et al. 1998, Balogh et al. 2003), but their effect on time lags also has not been adequately studied. 

Despite the difficulty in fully understanding and modeling the chemistry of mercury in the atmosphere, 

analysis of lake sediments does yield empirical evidence on mercury deposition. Because local 

geological sources of mercury are relatively rare, mercury in sediments of lakes that never received 

industrial discharges usually can be attributed to atmospheric deposition. In Minnesota, analysis of 

sediments accumulated in lakes over the past several hundred years allowed the following conclusions 

(Swain et al. 1992; Engstrom and Swain 1997; Engstrom et al. 1999): 

• About 70% of current mercury deposition in Minnesota is a result of anthropogenic 

emissions. 

• Annual atmospheric deposition as of 1990 was 12.5 micrograms per square meter per year 

(total of wet plus dry deposition). 

By comparing to sediment cores from coastal Alaska, we can attribute recent (1990s) atmospheric sources 

to Minnesota as follows: 30% natural from outside the state (e.g., volcanoes), 30% global pollution, and 

40% regional pollution (Engstrom and Swain 1997). Several recently published modeling studies (using 

different models) of global mercury cycling agree with this relative contribution from natural sources 

(Mason & Sheu 2002, Lamborg 2002, and Seigneur et al. 2004). 

Atmospheric deposition of mercury in some parts of Minnesota peaked in the 1970s, and has declined 

slightly since then. Wet deposition rates since 1996 (when mercury deposition network monitoring 

began) appear relatively uniform around the state, as shown by overlap in annual mercury deposition 

fluxes from fixed monitoring stations in Minnesota and Brule Wisconsin (Figure 8); the inset bar chart 

shows the station mean annual fluxes are not significantly different for the period 1996-2003. There is a 

significant precipitation gradient from northeast to southwest Minnesota, but this does not apparently 

determine the mercury deposition pattern. The uniformity in deposition indicates that sources causing 

locally elevated atmospheric deposition have been removed. Likely local sources include poorly 

controlled waste incineration, mercury fungicide use in paper making, and coal combustion in urban areas 

for space heating. 

Despite removal of many mercury sources, significant mercury emissions sources remain within 

Minnesota and contribute to mercury deposition in the state. Jackson et al. (2000) estimated that onequarter of the 40% regional pollution, or 10% of total deposition within Minnesota, is because of 

emissions within the state. The balance of the regional sources was attributed to the rest of the United 

States. 

Engstrom and Swain (1997) apportioned the 70% of atmospheric deposition that is anthropogenic into 

30% global and 40% regional, by comparing mercury increases in northern Minnesota to coastal Alaska. 

By assuming that Alaska is so far from sources that it represents global deposition (which is also a 

component of Minnesota’s deposition), and noting that Minnesota’s increase over natural is 3.4-fold, 

while Alaska’s increase is just 2.0-fold, one can calculate that in 1990 the source areas of Minnesota’s 

deposition was 30% natural global, 30% anthropogenic global, and 40% anthropogenic regional. 

Unfortunately, there was no way to know the exact geographic extent of the sources contributing to the 

regionally elevated mercury deposition. Jackson et al. (2000) apportioned the source region as follows, 

using qualitative knowledge of source strengths and likely transport distances: “...the United States is 

assumed to be the regional area that Engstrom and Swain determined contributes 40% of the deposition in 

Minnesota. The 40% is then subdivided: 10% being local deposition from Minnesota emissions; 15% 

MN Statewide Mercury TMDL 27MAR07_final.doc 20
from the rest of the Midwest and the remaining 15% from U.S. sources outside of the Midwest.” The 

10% proportion will decline over time as incinerators and other sources of divalent mercury are 

controlled. We expect that models of later emission years will show a lower and lower in-state percent 

contribution to overall deposition in Minnesota. 

0

2

4

6

8

10

12

14

1996 1997 1998 1999 2000 2001 2002 2003

g Hg km-2 yr-1

Marcell (MN16)

Fernberg (MN18)

Ripley (MN23)

Lamberton (MN27)

Brule (WI08)

Average

4 5 6 7 8 9 10 11

Marcell (MN16)

Fernberg (MN18)

Ripley (MN23)

Lamberton (MN27)

Brule (WI08)

Mean Annual Flux ± 95% C.I.(g km-2) for 1996-2003 

Figure 8 Annual Mercury Flux at Mercury Deposition Network (MDN) Sites in Minnesota 

The 10% in-state contribution is supported by atmospheric modeling of mercury for a domain that 

includes the continental United States, southern Canada, and northern Mexico (Atkinson, 2003). For 

Minnesota, the USEPA modeling showed total annual emissions of mercury from Minnesota were 2571 

kg in 1998, and 586 kg were deposited within the domain. According to model results, of the 586 kg of 

mercury, 48% (281 kg) was deposited within the state, which is 10.9% of the 2571 kg emitted by the 

state. Model results showed annual atmospheric mercury deposition in Minnesota was within the range 

of 10 to 30 g/km2

, which is 2200 to 6600 kg/y for the whole state. The 281 kg deposited by Minnesota 

sources, therefore, represents 4% to 13% of the total deposition to the state. Thus, the 10% estimated 

state contribution to mercury deposition within the state, from Jackson et al. (2000), is within the 

bracketed range from USEPA’s model results. 

One concern when evaluating mercury sources is the likelihood of “depositional hotspots” where mercury 

deposition far exceeds the norm. Engstrom and Swain (1997) discuss sediment data that show greater 

mercury loading in 1990 to lakes in urban Minneapolis and agricultural areas of western Minnesota, 

compared to northern Minnesota (findings confirmed by later unpublished sediment core work). 

However, it is uncertain if the greater loading is delivered by the atmosphere. In agricultural areas, the 

mercury load to lakes is likely enhanced by soil erosion. In urbanized areas, the mercury load may have 

been enhanced by development of impervious surfaces or indirectly from the use of mercury-preserved 

latex paints. Regardless of the indication of some historical localized higher mercury loading rates, there 

is no evidence of subsequently higher fish mercury levels (i.e., no biological hotspots). 

MN Statewide Mercury TMDL 27MAR07_final.doc 21
An alternative to sediment core data as the basis for total mercury deposition is computer modeling. 

There has been no effort to correlate Minnesota’s fish concentrations to any atmospheric modeling, such 

as that of Atkinson (2003). There is a great deal of variation in fish concentrations from lake to lake, even 

in rural areas far from emission sources that receive equal atmospheric mercury deposition. We know 

that the average mercury concentrations of fish in the Minneapolis-St. Paul metropolitan area are not 

significantly different from concentrations in the rest of the SW region. Even though lake to lake 

variation is greater than any increment because of urban deposition, our working assumption is that the 

mercury concentrations of fish in all lakes will decline when a steady state is approached after the 

atmospheric loading is reduced. The EPA model output (Atkinson, 2003) shows greater deposition near 

Minneapolis for the 1998 emission year. The greater deposition was driven by two incinerators in 

Goodhue County, a rural area over 40 miles southeast of Minneapolis. By 2000, mercury emissions from 

these facilities were reduced from about 300 pounds to less than 5 pounds per year. 

In the 1990s there were three incinerators operating in Goodhue County, one in Cannon Falls, and two in 

Red Wing. Lake and stream data for mercury are sparse in the Goodhue County area, largely because 

there is not much surface water aside from the Mississippi River and some tributaries. One tributary, the 

Cannon River, flows in an easterly direction in Rice County and then flows into Goodhue County, near 

the northern county line. The Cannon River discharges into the Mississippi about 5 km NE of the city of 

Red Wing, the site of the other contributing incinerator. The headwater reaches in Rice County are 

impaired, and listed for excess mercury in fish. In addition Byllesby Reservoir is listed as impaired 

because of fish that were sampled in the 1980s. Byllesby Reservoir is adjacent to the city of Cannon 

Falls, the location of one of the two incinerators that contributed to the modeled elevated mercury 

deposition. However, the incinerator did not start operating until the 1990s, after the fish were sampled. 

The Cannon River between Byllesby Reservoir and Welch, MN was sampled in 1992 and the fish (carp, 

smallmouth bass, and walleye) were not impaired and these reaches are not listed for excess mercury. 

One basic tenet of the TMDL program is to make the best TMDL possible with the data available. Our 

available fish data, albeit sparse in some locations, do not support the presence of a hotspot in terms of 

fish mercury concentrations in Goodhue County. Once the reduction goals are established, a phased 

adaptive watershed management approach will re-assess subsequent data as needed. 

Minnesota

Mercury Emissions (2000)

Coal 46%

Petroleum 5%

Wood 0.3% Natural gas 0.0% 

Volatilization from disposed products 7%

Municipal solid waste combustion 5%

Smelters that recycle cars and appliances 5%

Sewage sludge incineration 3%

Dental preparations 3%

Crematories 2%

On-site household waste incineration 2%

Recycling mercury from products 1.4%

Fluorescent lamp breakage 0.9%

Medical waste incineration 0.2%

Taconite processing 21% 

Soil roasting 0.4%

Energy 51%

Material Processing 21% 

Purposeful Use 28%

Sources of Atmospheric 

Mercury Deposition to Minnesota

Natural

Emissions

30%

Global 

Emissions

30%

Regional

Emissions

40%

MN 

Emissions 

(~10%)

Minnesota

Mercury Emissions (2000)

Coal 46%

Petroleum 5%

Wood 0.3% Natural gas 0.0% 

Volatilization from disposed products 7%

Municipal solid waste combustion 5%

Smelters that recycle cars and appliances 5%

Sewage sludge incineration 3%

Dental preparations 3%

Crematories 2%

On-site household waste incineration 2%

Recycling mercury from products 1.4%

Fluorescent lamp breakage 0.9%

Medical waste incineration 0.2%

Taconite processing 21% 

Soil roasting 0.4%

Energy 51%

Material Processing 21% 

Purposeful Use 28%

Sources of Atmospheric 

Mercury Deposition to Minnesota

Natural

Emissions

30%

Global 

Emissions

30%

Regional

Emissions

40%

MN 

Emissions 

(~10%)

 

Figure 9 Sources of Mercury Deposition and Estimated Mercury Emission Sources in Minnesota 

Mercury from anthropogenic emission sources (i.e., emitted to the atmosphere because of human 

activities) is divided by the MPCA into three categories: (1) emissions related to energy production, (2) 

emissions because of purposeful use, and (3) emissions because of material processing (Figure 9). 

Although emissions from fossil fuel combustion and the processing of metal ores are both the result of the 

incidental release of trace contaminants of natural geological materials, we have placed them in separate 

categories (energy production and material processing, respectively). As of 2000, 51% of Minnesota’s 

mercury emissions are from energy sources, 21% from taconite processing, and 28% from purposeful 

uses. 

MN Statewide Mercury TMDL 27MAR07_final.doc 22
5.2 Principle of Proportionality for Mercury in Air and Biota 

Ideally, the link between emissions and mercury bioaccumulation in fish would be known quantitatively 

and the effect of a given reduction in emissions accurately modeled. Such models are under development. 

In the absence of a validated model that accurately incorporates the complexities of atmospheric 

chemistry, watershed transport, methylation, and bioaccumulation in fish; we rely on the following 

rationale (Jackson et al. 2000): 

a. A reduction in emissions from sources in a given source area (local, regional or global) results in 

a proportional reduction in the rate of deposition in Minnesota attributable to those sources. 

b. A reduction in deposition results in a proportional reduction in mercury loading to water bodies. 

c. Within a given water body, a proportional reduction in mercury loading in the water results in a 

proportional reduction in mercury concentrations in fish. 

For example, a 50% reduction in mercury emissions from Minnesota sources is projected to result in a 5% 

reduction in deposition in Minnesota (50% of 10% state share), and, therefore, a 5% reduction in mercury 

contamination of fish. A 50% reduction applied to anthropogenic global sources is projected to result in a 

35% reduction in deposition in Minnesota (50% of 70%), and, therefore, a 35% reduction in mercury 

contamination of fish. 

This assumption of proportionality between mercury deposition and fish bioaccumulation acknowledges 

that lakes differ in the proportion of atmospherically deposited mercury that is methylated and the 

efficiency that methylmercury is accumulated in fish. This is described below as the bioavailability 

factor. Proportionality assumes that these factors are constants, unaffected by the rate of atmospheric 

mercury deposition. 

A variety of physical processes could cause time lags, including delayed release of mercury from the 

terrestrial watershed around surface water, and release from sediments contaminated from earlier 

atmospheric deposition. However, mercury in terrestrial systems will eventually reach a new steady state 

with atmospheric deposition, and total loading of mercury to surface water will be proportional to 

atmospheric deposition. 

Similarly, sediments eventually will also equilibrate with atmospheric deposition, but perhaps through 

different mechanisms than do terrestrial soils. For example, if the sediment is in a depositional zone, 

new, cleaner sediments may simply cover up and bury the older, more contaminated sediment. 

Mechanistic models for mercury predict proportionality between atmospheric deposition and fish 

contamination. The Pilot Mercury TMDL exercise for the Florida Everglades found “The E-MCM model 

predicts a linear relationship between atmospheric mercury deposition and mercury concentrations in 

largemouth bass....The slight offset from a 1:1 relationship results from slow mobilization of historically 

deposited mercury from deeper sediment layers to the water column....” (Atkeson et al. 2002; Figure 10). 

Similarly, the EPA’s Mercury Maps project examined the MCM model and the IEM-2M watershed 

model, and found they both predict proportionality between atmospheric deposition and fish 

contamination (USEPA 2001d). The following approach follows the Mercury Maps discussion on the 

proportionality between change in atmospheric deposition and change in fish tissue concentration. The 

Mercury Maps report describes the relationship as 

( )

( ) 1, 1,

2, 2,

1,

2,

tair tother

tair tother

tfish

tfish

LL

LL

C

C

+

+ = (1) 

MN Statewide Mercury TMDL 27MAR07_final.doc 23
where, Cfish,t1 and Cfish,t2 are the mercury concentrations in fish at times 1 and 2, which could be the 

baseline and target concentrations; Lair,t1 and Lair,t2 are the air deposition Hg loads to a waterbody, 

including direct deposition and indirect deposition via the watershed; and Lother is loading from other 

sources. There are no known significant natural geologic sources of mercury in the state. For this 

mercury TMDL, the only other sources considered are wastewater discharges (NPDES permitted 

discharges). The wastewater sources are insignificant compared to air sources (See Section 6.3) and, 

therefore, drop out of the simplified equation. 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Fraction of Current Mercury Deposition (Lair,t2/Lair,t1)

Fraction of Current Fish Mercury Conc. 

(Cfish,t2/Cfish,t1)

E-MCM

Predicted

Proportional

Response

Figure 10 Proportionality between atmospheric mercury deposition and mercury concentrations 

as predicted by the E-MCM model for largemouth bass in the Everglades 

Atmospheric loading is the product of area and air deposition; total area can be split into water area and 

land area to distinguish direct atmospheric loading from indirect watershed loading. To account for 

mercury that is buried in the soil or volatilized to the atmosphere, the watershed loading can be 

discounted by a runoff coefficient, which remains constant for a given region as long as there are no 

significant changes in land cover/use. This was tested by comparing land cover changes between 1982 

and 1997 (http://www.mn.nrcs.usda.gov/technical/nri/tables/lcu_change.htm), applying standard runoff 

coefficients to each of the general land cover types. Although there were obvious increases in urban land 

use, the effect of the change was not significant to the composite runoff coefficient for the state: 

composite runoff coefficients were 0.289 for 1982 and 0.287 for 1997. 

The air deposition mercury loading can be described as 

( (2) air Ly +⋅⋅= ArADL W )

where Dy is the annual air deposition flux of mercury (g km-2

 y

-1); r is the runoff coefficient (also known 

as the delivery ratio); AL and AW are the areas of land and water (km2

). Assuming areas and r for each 

region do not change from t1 to t2, Substituting this definition of Lair into equation 1, areas will not change 

from t1 to t2 and, therefore areas drop out of the equation. In addition, we can include a bioavailability 

factor to account for the fraction of divalent mercury (Hg2+) converted to methylmercury (MeHg). 

Combining Equations 1 and 2, as well as, including the bioavailability factor, the relationship becomes 

MN Statewide Mercury TMDL 27MAR07_final.doc 24
1

2

1

2

1,

2,

1,

2,

t

t

t

t

ty

ty

tfish

tfish

b

b

r

r

D

D

C

C ⋅⋅= (3) 

where b is the bioavailability factor. An operational definition for b is the MeHg fraction of total Hg, 

because MeHg is the form of mercury that bioaccumulates; however, it could also include labile Hg2+ that 

is readily converted to MeHg. Bioavailability is influenced by a variety of factors that control 

methylation and MeHg mobility, such as wetland density, sulfate deposition, and dissolved organic 

carbon production. 

For the estimate of the TMDL for mercury, we are assuming r and b do not change over time; therefore, 

their t2/t1 ratios are equal to one, they can drop out of the equation, and Equation 3 simplifies to 

1,

2,

1,

2,

ty

ty

tfish

tfish

D

D

C

C = (4) 

We can rearrange Equation 4 to solve for a target atmospheric deposition (Dy), substituting the baseline 

and target values for the t1 and t2 values, respectively: 

baseliney

fish baseline

ettfish

etty D

C

C

D ,

,

arg,

arg, = ⋅ (5) 

To calculate a target atmospheric mercury load, we are not concerned with the values of r and b because 

we assumed they do not change over time; however, it is plausible that r and b could change. We can 

consider what affect changing these coefficients will have on achieving the target fish tissue 

concentration. The combined effect of r and b determines how much Hg is available for uptake by the 

aquatic food chain. We expect r to be greater in the SW region than in the NE region and the converse 

for b. In other words, in the SW waters, such as the Minnesota River, we expect a high transport rate of 

Hg off the watershed, but a small fraction of that runoff Hg is bioavailable; whereas, in the NE, we expect 

a low transport rate, but a high fraction of bioavailable Hg. 

Neither proportionality, nor any other model, is able to deal accurately with short-term perturbations in 

equilibrium, such as accelerated erosion of soil that contains mercury from past atmospheric deposition. 

It is not clear, for instance, whether the mercury associated with eroded soil is just as likely to become 

methylated as other sources of mercury. New research suggests that more recently deposited mercury is 

more bioavailable (Hintelman et al. 2002). Nevertheless, intentional reduction of r through watershed 

best management practices could contribute to load reductions. This is reasonable for the SW region, 

where we have evidence of Hg associated with suspended solids, but not the NE region, where Hg is more 

often associated with dissolved solids (i.e., dissolved organic matter). On the other hand, fish mercury 

concentrations in the NE region could be reduced by reducing b via reduced air deposition of sulfate, 

which can reduce methylation rates by reducing the activity of sulfate reducing bacteria (See Section 5.4). 

Reducing sulfate deposition is not likely to have an effect in the SW region because sulfate concentrations 

are relatively very high and wetland acreage has significantly decreased over the last 100 years. 

Although there is little research on the interaction of r and b, it is likely that in SW Minnesota, r and b are 

not entirely independent of each other. For example, when r is high, soil erosion delivers suspended 

solids and phosphorus, as well as mercury, to the surface water. These materials probably reduce 

bioavailability (b) of Hg. The suspended solids sorb divalent mercury, perhaps reducing interaction with 

methylating bacteria. Greater phosphorus increases the biomass of all levels of the food chain, decreasing 

the concentration of methylmercury in fish (i.e., biodilution). 

MN Statewide Mercury TMDL 27MAR07_final.doc 25
We can also consider a change in the loading from the “other” sources. Point sources are treated as 

insignificant in the loading calculations, but they could be included in the equation for the sake of 

discussing potential reductions in point source loads. Point source loads are the product of discharge flow 

and mercury concentration. It is likely that the average mercury concentrations in many wastewaters will 

be reduced in the future through changes in dental practices and improved wastewater treatment methods, 

such as “Bio-P” and “Chem-P,” which reduce mercury concentrations in the effluent by reducing solids 

(G. Kimball, MPCA; personal communication). 

5.3 Trends in Mercury Emissions and Deposition 

5.3.1 Trends in Use and Emission of Mercury 

While some of the mercury used in products is recycled and reused, some is released into the environment 

when it is spilled or when it is disposed of in a drain or garbage. Historically, many intentional uses 

presumed mercury dissipated into the environment and was not harmful (e.g,. fungicides: seed coatings, 

golf course treatments, latex paint preservatives). As understanding about the bioaccumulation of 

mercury in the aquatic food chain grew, these uses of mercury were banned. 

Mercury use peaked in the 1960s in the United States at more than 2,000 metric tons per year and by 1990 

declined significantly to about 600 metric tons (Figure 11A; Engstrom and Swain 1997). Worldwide 

consumption followed this same pattern ((Hylander and Meili 2003). U.S. industrial consumption of 

mercury has consistently been about 25% of global production of mercury (Engstrom and Swain 1997). 

As noted above, only a portion of the mercury consumed in manufacturing and products is emitted to the 

atmosphere. However, mining and the use of mercury was historically conducted on such a massive scale 

that if only 10 to 15% of this mercury were emitted, it would easily exceed mercury emissions from other 

sources. In Figure 11A one can see that the mercury used as fungicides in agriculture, paper, and paint 

totaled about 400 metric tons in 1970, and presumably all volatilized to the atmosphere within a few 

years. Compare that total to the mercury content of coal (Figure 11B), which approaches 80 metric tons 

in the 1990s, of which about 50 tons were emitted (USEPA 1997). Given the significant decline in 

mercury use, one would expect mercury emissions to have declined significantly in recent years. 

Future mercury emissions from manufacturing and fuel combustion are expected to decline worldwide. 

Pirrone et al. (1996) concluded that on a global basis, total anthropogenic emissions of mercury peaked in 

1989 at about 2,290 metric tons, and have been decreasing at the rate of about 1.3% per year. Use of 

mercury in manufacturing and products will continue to decline world wide, resulting in lower emissions. 

Mercury emissions associated with coal combustion are also expected to eventually decline worldwide; 

however, growth in Asia may significantly delay the expected reductions. 

A historical reconstruction of emissions in the United States from 1930 to 2000 (Figure 12; Pollman and 

Porcella 2002) shows a significant decline in total mercury emissions since about 1980, accelerating after 

1990 because of the elimination of mercury from latex paint. The pattern was also seen in mercury 

emissions from 1870 to 2000 in Maritime Canada (Sunderland and Chmura 2000). Therefore, the 

amounts of mercury used and released in Minnesota, the United States and the rest of the world have 

undoubtedly been cut dramatically over the past few decades. 

MN Statewide Mercury TMDL 27MAR07_final.doc 26
Total

Utility 

0

500

1,000

1,500

2,000

2,500

3,000

Othe r

Control Instruments

Electrical Appara tus

Pha rma ce uticals

Dental

Chlor-Alka li

Paint

Agriculture/Paper

0

0

20

40

60

80

0

200

400

600

800

1900 1920 1940 1960 1980 2000

YEAR

Industrial

Mercury

Consumption

(metric tons)

Coal

Combustion

(millions 

of metric tons)

Mercury 

In 

Coal

( metric tons)

A

B

Figure 11 Mercury Consumption in the United States 

Figure 12 United States Mercury Emissions by Category 

Annual mercury releases, as of 2000, in Minnesota are about one-third what they were in 1990 (See 

MPCA 2005). Current MPCA estimates indicate that statewide releases in 2000 were about 1,650 kg 

(3,638 lb), 68% below estimated 1990 levels (Figure 13). Nearly all reductions since 1990 are because of 

product-related uses: restricting the intentional use of mercury in products such as paint and batteries, 

improved management and substitution of mercury-containing products (thermostats, fluorescent lamps, 

etc.), reduction in uncontrolled incineration, and emission controls on waste-combustion facilities. 

MN Statewide Mercury TMDL 27MAR07_final.doc 27
724 756 759 679

8,881

1,738 1,045 671

1,667 1,779 1,834 1,825

0

2,000

4,000

6,000

8,000

10,000

12,000

1990 1995 2000 2005

(projected) Year

Mercury (pounds)

Product Use & Disposal

Other (mostly taconite production)

Energy (mostly coal and oil)

68% Reduction from 1990

70% Reduction from 1990

Figure 13 Minnesota Statewide Mercury Emissions Trend by Source 

Given existing trends in decreased use of mercury in products, increases in mercury-product recycling 

and controls on sewage-sludge incinerators, the MPCA expects emissions to continue to decline, falling 

below 70% of 1990 levels by 2005. Taconite data shows an increase of 4.8% from 1990 to 2000, and 

energy production shows an increase of 10.0% over that time period. Because of an 88% decrease in 

mercury emissions from Product Use and Disposal, a much bigger category, there was an overall decrease 

of 68% in Minnesota Hg emissions from 1990 to 2000. Because of this large overall decrease, and 

because both of these sectors mostly emit elemental mercury (about 90% elemental), we do not expect 

any noticeable effect of these modest increases on local deposition or mercury concentrations in fish. 

These increased emissions are calculated into the state’s overall trend since 1990, and do not affect the 

establishment of the 1990 baseline. This information will, however, be a key component of subsequent 

implementation planning. 

Anthropogenic emissions in the U.S. have decreased 45% between 1990 and 1999, according to the 

USEPA (Figure 14). This mercury emissions summary does not include area sources, such as latex paint 

and fungicides, which are included in the Minnesota Mercury Emissions Inventory (MPCA 2005). 

Before the USEPA banned the use of mercury in interior paint in 1990 and exterior paint in 1991, the 

paint sector was using 150-350 tonnes per year. Mercury was estimated to volatilize from paint at the rate 

of 75% per year (Barr Engineering 2001). In 1989, 211 tonnes (465,170 pounds) of mercury were used 

by the U.S. paint industry. Thus, if emissions from paint were included in the U.S. emissions summary, 

the 1990 emissions estimate would be much larger and the decline in mercury emissions would be much 

larger than the 45% decline show in Figure 14 (USEPA 2004). 

MN Statewide Mercury TMDL 27MAR07_final.doc 28
0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

500,000

1990 1996 1999

Year

Mercury (pounds)

Other

Institutional Boilers

Gold Mines

Chlorine Production

Hazardous Waste Incineration

Medical Waste Incinerators

Municipal WasteCombustors

Utility Coal Boilers

Source: Fish Advisories Briefing FINAL 082404v1.ppt; 

EPA 1990, 1996 NTI and EPA 1999 NEI. Short tons 

per year. Adjusted for gold mines in 1990 and 1996.

Figure 14 USEPA's anthropogenic mercury emissions in U.S. 

5.3.2 Trends in Atmospheric Deposition of Mercury 

A number of lines of evidence support the conclusion that atmospheric mercury has declined because of 

decreased mercury use and emissions. An analysis of air concentrations from around the world since the 

1970s shows significant decreases of about 20% since about 1990 (Slemr et al. 2003). 

Lichens and mosses have been used to monitor atmospheric mercury concentrations. Utilizing lichens in 

a national park in North Dakota as a natural collector of atmospherically deposited metals, Bennett and 

Wetmore (2000) found that mercury concentrations decreased by about 30% from 1983 to 1998. Based 

on nationwide surveys of moss as a collector of atmospheric deposition of metals, Steinnes et al. (2003) 

showed that mercury concentrations in 2000 were 30% lower than they had been in 1985. 

Evidence of declines from contemporaneous measurement of mercury in precipitation is more 

problematical because mercury deposition is highly dependent on the quantity of precipitation, which 

varies significantly from year to year. The statistical effect of precipitation variability should become less 

once a few decades of data are collected. Unfortunately, a permanent, long-term national monitoring 

program — the Mercury Deposition Network (http://nadp.sws.uiuc.edu/mdn/) — was not begun until 

1995. In a monitoring program funded by the State of Minnesota, Glass and Sorensen (1999) saw slight 

increases in mercury deposition in the Upper Midwest from 1990 to1995. Between 1994 and 1999, with 

a different monitoring program, Watras et al. (2000) reported a 40% decrease in mercury deposition in 

northern Wisconsin. 

The initial evidence that mercury deposition rates had decreased over the past few decades came from 

sediment cores from a number of lakes in Minnesota (Engstrom and Swain 1997), although there was not 

yet evidence for global declines. Sediment core studies from lakes in Minnesota and elsewhere show 

slight declines in atmospheric deposition relative to a peak in the 1970s and 1980s. There is some 

evidence that concentrations of mercury in fish have also declined, but not to the point of eliminating 

MN Statewide Mercury TMDL 27MAR07_final.doc 29
concerns about fish consumption (see Section 5.6). But, it is encouraging that efforts to reduce the use 

and release of mercury appear to have resulted in measurable environmental improvement. 

e Mercury TMDL 27MAR07_final.doc 30

2002). 

Figure 15 Mercury Accumulation Record in the Fremont Glacier, Wyoming 

5.4 Interaction Between Sulfate Deposition and Mercury Methylation 

Further evidence for declines in midcontinental North America comes from the analysis of an ice core 

from the Fremont Glacier in the Wind River Range, Wyoming (Figure 15; Schuster et al. 2002). From 

this historical trend reconstruction, one can see the approximate magnitude of the pre-industrial (or 

natural) background level of mercury cycling through the environment, and spikes in mercury caused by 

events such as volcanoes. The ice core record shows a distinct decline since the 1980s. Evidence of 

declines in atmospheric deposition of mercury in New England has been found from bog cores in Maine 

(Norton et al. 1997) and multiple lake cores in Vermont and New Hampshire (Kamman and Engstrom 

Mercury contamination of fish is expected to be proportional to atmospheric deposition of mercury if the 

proportion of mercury that is methylated is constant. However, it is likely that the proportion has 

increased, relative to natural levels, because of other anthropogenic changes. Sulfate-reducing bacteria 

(SRB) have been shown to be responsible for most of the transformation of deposited mercury into

methylmercury. Atmospheric deposition of sulfate is thought to have stimulated the activity of SRB in 

geographic areas that are naturally sulfate-poor and, therefore, have increased the proportion of mercury

that is methylated (Gilmour and Henry 1991, Gilmour et al. 1992, Branfireun et al. 1999, Jeremiason et 

al. 2003, Jeremiason et al. 2006). 

MN Statewid
Therefore, it is possible that decreases in sulfate deposition as a result of the Clean Air Act of 1990 may 

decrease the efficiency of mercury methylation. Accordingly, we would expect two synergistic forces 

working to decrease mercury concentrations in fish: (1) decreased mercury deposition and (2) decreased 

y in fish from Little Rock Lake (in northern 

Wisconsin) decreased by roughly 30% between 1994 and 2000 because of decreased atmospheric 

ad 

ing 

from 

WWTPs) that discharge to Minnesota’s 

Ps discharge to receiving waters covered under this 

gion and 67 in the NE region (Appendix B). Most of the 

-fired 

e 

 be added to the waste stream and a conservatively estimated 1% 

is from drinking water. USEPA (2001d) reported the Association of Metropolitan Sewerage Agencies 

sis 

y 

 stormwater source water is 

precipitation runoff. As such, the relative percentages of background source and direct anthropogenic 

rict 

ee if 

ate a significant direct anthropogenic 

source in urban areas that is not seen in rural areas. Measurements of mercury concentrations in runoff 

002 

activity of the sulfate-reducing bacteria that methylate mercury. This synergism is a margin of safety 

because it is not factored in to the TMDL calculations 

As noted above, northern Wisconsin has seen a 40% decrease in mercury deposition. In a more recent

study, Hrabik and Watras (2002) concluded that mercur

mercury deposition, and 5% because of decreased atmospheric sulfate deposition (30% in a basin that h

been isolated and acidified as an experiment). An ongoing study in northern Minnesota includes add

sulfate to a wetland and the response has been increased methylmercury concentrations and export 

the wetland (Jeremiason et al. 2003, Jeremiason et al. 2006). 

5.5 Point Sources to Water 

There are 580 NPDES permitted wastewater treatment plants (

mercury impaired waters; 270 of those WWT

statewide mercury TMDL: 203 in the SW re

dischargers are publicly owned treatment works (POTWs). In addition, the following facilities were 

included in the point source mercury load estimates: NE region has one electricity-generating coal

power plant, four pulp & paper mills, and seven taconite processing facilities; the SW region has two 

electricity-generating coal-fired power plants and one petroleum refinery. Other major NPDES 

discharges are cooling water, which do not contain added mercury and were, therefore, not included in th

point source mercury load estimates. 

Wastewater is comprised of source water and anthropogenic wastewater inputs. Essentially all the 

mercury (99%) in WWTPs is assumed to

(AMSA) had done a study of 24 POTWs in six states, using clean techniques for sampling and analy

that reported a median mercury concentration of 5.0 ng/L in POTW effluents. MPCA has requested 

similar monitoring from 37 NPDES facilities (POTWs and industrial) in Minnesota; the central tendenc

of mercury concentrations in effluent has been in the range of 4 to 6 ng/L; therefore, 5 ng/L was used as 

the typical mercury concentration for NPDES facilities in Minnesota. 

Stormwater is considered wastewater as well, and is comprised of source water (atmospheric deposition) 

and direct anthropogenic inputs (wastewater). Unlike other wastewater,

sources are approximately opposite the WWTP influent proportions and essentially all mercury in 

stormwater is attributed to source water (See Section 6.2). The Western Lake Superior Sanitary Dist

has been doing detailed evaluations of mercury influents for a decade and stormwater has not been 

identified as a mercury source to the POTW (WLSSD 1997). 

The MPCA compared mercury concentrations in runoff from cultivated land and urban land use to s

the latter had higher mercury concentrations, which would indic

from agricultural field snowmelt and urban stormwater runoff are very limited. In 1996 and 1997, two 

studies measured snowmelt runoff from agriculture fields (Balogh et al. 2000; Sloan et al. 2001). In 2

and 2003, the Minneapolis Park and Recreation Board (MPRB) conducted a pilot study of mercury in 

stormwater at two locations (one residential and one industrial) for the Minneapolis-St. Paul NPDES 

Municipal Stormwater Permit. Mercury and total suspended solids grab samples were collected at the 

two sites during storm events. The median mercury concentration for agriculture runoff was 19.1 ng/L

and the median for the urban runoff (i.e., stormwater) was 21.7 ng/L. Considering that the measured 

agriculture runoff was only snowmelt, whereas the urban runoff data included storms throughout the 

MN Statewide Mercury TMDL 27MAR07_final.doc 31
summer, more overlap in agriculture and urban mercury concentrations would be expected if the 

agriculture runoff included runoff from summer storm events. These results indicate there is no 

significant difference between agricultural and urban stormwater runoff; therefore, the additional merc

contribution to stormwater from sources other than atmospheric deposition is essentially zero. In 

words, wet and dry deposition account for all of the mercury observed in stormwater and there ar

significant direct anthropogenic sources of mercury added to the stormwater. 

MPCA also has data for mercury concentrations in taconite processing facilities effluents. Based on th

state’s NPDES discharge monitoring database, a typical mercury concentration 

ury 

other 

e no 

e 

for effluent from these 

facilities is 1.5 ng/L. USEPA (2001d) reported average mercury concentrations in effluent from pulp & 

ed 

e discharge on the immediate receiving water. 

Although theoretically an issue in Minnesota, there is no documented case of locally elevated fish 

5.6 Environmental Trends 

l Minnesota surface waters 

sition of 

of 

ional and 

n 

l 

ve 

cales (i.e., local, regio

evidence includes changes in the mercury concentrations in sediment, ice co

ion 5.1). 

d 

 and elsewhere. Sulfate 

deposition can stimulate the activity of sulfate-reducing bacteria (SRB), which are responsible for the 

paper mills of 13 ng/L; therefore, this value was used in mercury loading estimates in 1990 because 

insufficient information for Minnesota mills. Recent monitoring from Boise Cascade had average 

mercury concentrations of 1.6 ng/L and data collected from Wisconsin paper mills showed an average 

effluent mercury concentration of 2 ng/L (Mugan 2005). 

The mercury contribution from a point source may be insignificant on a state, regional, or even watersh

scale, but there would remain the issue of the impact of th

contamination because of a point-source water discharge. Minnesota is building a database of mercury 

concentrations in wastewater effluent by relying on the wastewater treatment plant operators to routinely 

collect samples for mercury using clean techniques and low-level mercury analysis. 

5.6.1 Summary of Scientific Information 

Mercury contamination of fish in almost al

will ultimately reach a steady state with atmospheric depo

mercury. Therefore, changes in anthropogenic emissions 

atmospheric mercury that are deposited in Minnesota control changes 

in fish concentration. Sources of atmospheric mercury deposition to

Minnesota include natural (about 30% of total) and local, reg

global anthropogenic sources (totaling the remaining 70%). To the 

extent that emissions from these three geographic categories are 

reduced, fish contamination in Minnesota will also be reduced, 

although, (a) reductions in sources farther from Minnesota will have

correspondingly less benefit and (b) lag times of unknown duratio

will occur because of delayed release of mercury from terrestria

systems and release from contaminated sediments. 

According to emission-inventory reports, emissions of mercury ha

been significantly reduced on all three geographic s

Ed Swain adjusting experimental 

sulfate addition to a wetland 

nal, and global). Supporting 

res, moss and lichens, and 

changes in air concentrations from remote areas of the globe (See Sect

In addition, reduced sulfate deposition because of mandated controls sulfur dioxide emissions is expecte

to magnify the benefit of reduced mercury deposition in many lakes in Minnesota

transformation of mercury into methylmercury, the form that bioaccumulates in fish (See Section 5.4). 

MN Statewide Mercury TMDL 27MAR07_final.doc 32
5.6.2 Predicting Response Time 

The Everglades ecosystem differs significantly from aquatic systems in Minnesota, but the principle of 

proportionality between atmospheric mercury deposition and fish mercury concentrations is expected to 

hold in any ecosystem that does not have local geological sources. In the Everglades, the E-MCM model 

predicted slow recovery after reductions in atmospheric deposition because macrophyte roots mobilized 

historically deposited mercury from sediment as deep as 48 cm. Atkeson et al. (2002) found that even 

after 200 years of model simulation, deep sediment layers had not fully adjusted to changes in mercury 

loadings in the system, and continued to supply Hg(II) and methylmercury to the overlying system. After 

running simulations for 200 years with current loads to approximate steady state, they reduced 

atmospheric deposition as a step function and continued the simulation for an additional 200 years. 

Modeling results indicated the time required to achieve 50% of the ultimate response is approximately 10 

years (Figure 15; Atkeson et al. 2002); 90% of the ultimate response is projected to occur within 30 years. 

Projections would, of course, vary for other ecosystems, but this modeling exercise does give an idea of 

the response time following reductions in atmospheric mercury deposition. 

Figure 16 Predicted Dynamic Responses of Fish Tissue Mercury Concentrations Following 

Reductions in Mercury Deposition 

5.6.3 Trends in Fish Contamination 

Declines in mercury emission and deposition should result in reduced mercury concentrations in fish. 

There is evidence of lowered fish contamination levels from Minnesota, Wisconsin (Hrabik and Watras 

2002) and Florida (Atkeson et al. 2002). Mercury in fish is difficult to monitor and communicate as a 

uniform measurement because concentrations vary by species and size. Nevertheless, it is possible to 

monitor temporal trends in fish contamination by monitoring a single fish species, and, within that 

species, normalizing to a standard length. For example, in Little Rock Lake, Wisconsin, Hrabik and 

Watras (2002) documented that mercury in fish decreased by roughly 30% between 1994 and 2000, 

mostly because of decreased atmospheric mercury deposition and partly because of decreased sulfate 

deposition. There is also evidence that mercury concentrations in largemouth bass in the Everglades have 

declined in response to lower mercury deposition (Atkeson, pers. com.). 

MN Statewide Mercury TMDL 27MAR07_final.doc 33
In Minnesota, spatial and temporal trends in fish mercury concentrations have been examined using the 

fish tissue concentration in standard size northern pike and walleye. Results discussed in Section 4.3 

demonstrated significantly higher mercury concentrations in northern pike and walleye in the NE region 

compared to the SW region. Lakes in the NE region tend to have lower pH, lower conductivity and higher 

color (i.e., dissolved organic carbon). 

Another approach to looking at temporal trends in standardized fish tissue mercury concentrations has 

been on an individual lake basis. Changes over time in fish mercury concentrations within lakes were 

evaluated by comparing a recent sample year to an earlier year, which were at least five years apart. 

Recent sample years were 1995 or later and at least three fish (or composites) were analyzed each year. 

Of the 176 lakes meeting these criteria, 87 lakes (49%) showed a decrease in mercury concentrations, 45 

lakes (26%) had increased fish-Hg, and 44 lakes did not show a significant difference between years 

(Figure 17). A Chi-square statistical test shows that significantly more lakes declined in fish 

contamination than increased (p<0.01). 

87

44 45

0

10

20

30

40

50

60

70

80

90

100

Decreased Increased No Change

# of Lakes

Lake Selection Criteria:

1. Last collection 1995 or later

2. At least 5 years between collections

3. More than 2 samples per lake each year

4. Hg vs. fish length regression slope >0

Figure 17 Comparison Between Recent and Historical Fish Mercury Levels in 176 lakes (Northern 

Pike and Walleye; Standard Lengths) 

Selecting only the lakes with an historical collection around 1990 and a recent collection around 2000, the 

average change in fish mercury concentration was -11%; in other words, during the decade of the 1990s, 

there was a general decline in fish mercury concentrations of slightly more than one percent per year. 

Although it is not possible to relate the 68% reduction in state mercury emissions to this reduction in fish 

mercury levels during the same period because of the unknown response time, it does indicate there have 

been noticeable reductions in fish mercury levels that correspond with reductions in mercury emissions 

and deposition. The MPCA has a goal to continue that trend through the next decade (i.e., 10% reduction 

in fish tissue Hg concentration by 2010 compared to 2000). 

MN Statewide Mercury TMDL 27MAR07_final.doc 34
6 TMDL Development 

6.1 TMDL Formulation 

The TMDL formulation used for these regional mercury TMDLs is similar to the approach used in the 

EPA-approved TMDL for the Ouachita River Basin, Arkansas (FTN 2002, FTN 2003). The Ouachita 

TMDL for lakes (FTN 2003) has a section, “TMDL Formulation,” in which they define TMDL= (EL/RF) 

x SF, where EL is total existing load, RF is reduction factor, and SF is site specific factor. The Minnesota 

Mercury TMDL, Equation 6, uses the concept of total existing load (we call it “total source load”) and 

reduction factor to define the needed TMDL. SF is not used in Equation 6, but the concept of a variable 

for site-specific factors was used previously (Section 5.2) with the introduction of runoff coefficient (“r”) 

and bioavailability factor (“b”). As discussed previously, these factors cancel out of the equation that 

shows the change in fish tissue mercury is proportional to the change in deposition is proportion. 

Annual loads are more appropriate than daily loads for mercury because the concern in this TMDL study 

is the long term accumulation of mercury rather than the short term acute toxicity events. The three-step 

process to determine the TMDL is (1) estimate existing load for point and nonpoint sources; (2) define the 

target loads; and (3) calculate load reduction factors necessary to achieve target values. The total source 

load and reduction factor are then combined to give the total maximum daily load in units of mass per 

time. 

⎟

⎠

⎞ ⎜

⎝

⎛ −⋅=

100

1 RF TMDL TSL (6) 

where, TMDL is total maximum daily load as an annual load (kg/yr); TSL is total source load during the 

baseline year; RF is the reduction factor, as a percentage. RF is based on the reductions needed to 

achieve target fish mercury concentrations (see Section 4.4). The RF accounts for differences in mercury 

transport and bioavailability of the estimated load for each region (see Section 5.2). Ultimately, the 

TMDL is presented in the basic equation form. 

TMDL ++= MOSLAWLA (7) 

where, WLA is Wasteload Allocation (wastewater & stormwater sources), LA is Load Allocation 

(nonpoint sources), and MOS is Margin of Safety. Each of these TMDL components is discussed below. 

6.2 Baseline Mercury Load for 1990 

Total Source Load (TSL) of mercury, in kg/yr, is simply the sum of point source and nonpoint source 

loadings. 

PSLTSL += NPSL (8) 

where PSL is point source load and NPSL is nonpoint source load. PSL is estimated for each region 

based on the facilities total design flow and the average effluent mercury concentration. 

CQPSL avgi ∑ ⋅= (9) 

where Qi is the design flow for each permitted facility and Cavg is the estimated average mercury 

concentration in effluent (Table 7). Wastewater treatment plants (WWTPs) were separated into the two 

regions and their design flows were summed for each region for the wasteload calculations. A state 

average mercury concentration for wastewater effluent was used in the wasteload calculation, because the 

wastewater effluent was not considered different between regions. The design flow is a conservative 

assumption of WWTP mercury load because actual discharges are approximately 70% of design flows 

MN Statewide Mercury TMDL 27MAR07_final.doc 35
and very few WWTPs achieve their design flow. The current discharge information was used for the 

wastewater treatment plant design flow. Actual wastewater discharge has undoubtedly increased since 

1990, with increasing population; however, the design flow is not considered an excessive overestimate 

because the number of wastewater treatment plants has not changed significantly since 1990 (see Section 

5.5). A drinking water correction factor was applied to the point source load calculation to account for 

the one percent of influent to a wastewater treatment system that consists of drinking water. This one 

percent is not given as a credit because the 1990 total point source load was only 1.2% of the total 

mercury load. 

Table 7 Mercury Load Inputs and Estimates for 1990 

SW NE 

(a) WATER 

Metro 

WWTP 

Other 

WWTPs Total 

WLSSD 

WWTP 

Other 

WWTPs Taconite 

Pulp & 

Paper Total 

No. Point Sources 1 515 516 1 98 19[3] 4 122 

Mean Effluent Mercury 

Conc. (ng/L) 11 5 355 5 1.5 13 

Sum of Design Flows 

(mgd) 251 455 706 49 46 169 82 346 

PS Mercury Load 

(kg/yr)[1][2] 3.8 3.2 7.0 23.7 0.7 0.3 1.5 26.2 

(b) ATMOSPHERE SW NE 

Atmospheric Deposition (g km-2 yr-1) 12.5 12.5 

Region Area (km2) 129,674 90,151 

NPS Mercury Load 

(kg/yr) 1,621 1,127 

(c) SUMMARY (kg/yr) SW NE 

Point Source Load 

(PSL) 7.0 26.2 

Nonpoint Source Load (NPSL) 1,621 1,127 

Total Source Load 

(TSL) 1,628 1,153 

[1] Effluent - drinking water correction factor is 0.99 

[2] Anthropogenic sources to stormwater are included but the load is zero. Stormwater from precipitation is 

accounted for in the nonpoint source load. 

[3] Seven taconite facilities each have 2-3 NPDES permits; 15 of the 19 facilities have design flows greater than 

0.05 mgd. 

Stormwater, if addressed in a TMDL, is usually included with the point source load and included in the 

wasteload allocation (see Section 5.5). Because the source of most mercury to stormwater is atmospheric 

deposition—the same as for nonpoint source loads—the atmospheric deposition source of mercury to 

stormwater is accounted for in the nonpoint source load calculation. The contribution of mercury from 

other sources to stormwater is accounted for in the wasteload calculation and is estimated to be 

insignificant (i.e., estimated as zero). 

The only significant nonpoint source load (NPSL) is from atmospheric deposition: 

 (10) SADNPSL ry ⋅=

MN Statewide Mercury TMDL 27MAR07_final.doc 36
where Dy is atmospheric deposition (g km-2 yr-1) and SAr is regional surface area. The atmospheric 

mercury deposition for 1990 was 12.5 g km-2 yr-1. The SW region covers 59% of the approximately 

220,000 km2

 in Minnesota. 

Based on these calculations of point source and nonpoint source mercury loads, the 1990 TSL was 1628 

kg/yr for the SW region and 1153 kg/yr for the NE region. PSL was 0.4% of the SW region baseline load 

and 2.2% of the NE region baseline load. Combined, the water point sources contributed 1.2% of the 

baseline mercury load to the state’s waters in 1990. 

6.3 Wasteload Allocations (WLA) 

The calculated allowable load (TMDL) of mercury that will not cause an exceedance of the applicable 

water quality standard is the sum of the load allocation (atmospheric deposition) and wasteload 

allocations (NPDES sources); therefore, the total allowable load must be apportioned between the 

atmospheric and wastewater point source loads. For both regions combined, the PSL was 1.2% of the 

total source mercury load. Clearly, all significant decreases in mercury loading will come from 

reductions in atmospheric deposition (i.e., load allocation). Therefore, the WLA is set at one percent of 

the TMDL or the 1990 PSL, whichever is lower. The resulting WLA is 4 kg/yr for the NE region and 7 

kg/yr for the SW region. Assigning one percent to the WLA is equivalent to the cutoff USEPA’s 

Mercury Maps model used to screen watersheds for significant point source impact (USEPA 2001d). 

The WLA is by region and is not specific to each source, thereby providing a cap for the region that 

includes reserve capacity. Rather than assign an allocation to each source based on their current design 

capacity, continued mercury reduction will be encouraged through mercury minimization plans and 

enhanced phosphorus removal. EPA has determined, as a matter of policy, that NPDES point sources 

known to discharge mercury at levels above the amount present in the source water should reduce their 

loadings of mercury using appropriate, cost-effective, mercury minimization measures to ensure that the 

total aggregate point source mercury discharges are at a level equal to or less than the WLA specified in 

this TMDL. The reserve capacity in the WLA allows for permitting of additional wastewater discharges, 

but does not preclude the requirement of mercury minimization plans. 

There are no known local hotspots. The MPCA looked at possible impacts from large water and air 

sources and did not see local impacts in elevated fish mercury concentrations compared to the background 

regional levels. The concern for local impacts from wastewater discharges are primarily where they 

discharge to effluent dominated streams (i.e., the dilution ratio is less than 10:1). In those cases, the 

NPDES permit requires stringent controls for solids and BOD removal. In the most restrictive cases the 

CBOD-5 limit is 5 mg/L. These restrictive effluent limits to protect receiving waters have the added 

benefit of low mercury concentrations in the effluent because most of the mercury is associated with 

solids. The MPCA has mercury data on two POTWs that have CBOD-5 limits of 5 mg/L. The mercury 

concentrations from these facilities are the two lowest values in a dataset of 30 POTWs: 0.90 ng/L and 

1.30 ng/L. 

There is an increasing use of the “Bio-P” process to meet 1 mg/L phosphorus effluent limits in 

Minnesota; at least 25 Minnesota facilities will be using it within their current permit cycle. This process 

greatly reduces solids and in so doing reduces mercury discharge. The MPCA has mercury 

concentrations from three facilities currently using Bio-P; the average mercury concentrations at the three 

facilities are 2.56 ng/L, 3.26 ng/L, and 3.65 ng/L. The MPCA will propose for rulemaking in 2006 that 

new or expanding dischargers get the 1 mg/L limit for total phosphorus if they discharge more than 1800 

lbs TP per year. 

In keeping with the adaptive watershed management approach and as part of the TMDL implementation 

plan, the MPCA will continue to investigate potential local impacts of point sources in effluent dominated 

streams, and where warranted, look to additional permit limitations and then, if necessary, develop a sitespecific mercury TMDL. 

MN Statewide Mercury TMDL 27MAR07_final.doc 37
6.4 Load Allocations (LA) 

The total source load is the basis for the load allocation because all significant mercury load reductions 

are expected to come from atmospheric emission reductions. The regional reduction factors of 51% for 

the SW and 65% for the NE, multiplied by the total source loads yield mercury reductions of 830 kg/yr 

and 749 kg/yr, respectively (Table 8). Subtracting the load reduction goals from the baseline loads 

results in regional mercury load allocations of 798 kg/yr for the SW and 404 kg/yr for the NE. The 

needed reductions are similar for the two regions, but the mercury load allocation for the NE region is 

about one-half the SW region’s load allocation. 

Table 8 Mercury Load Reductions for Each Region 

Region 

SW NE 

Total Source Load (kg/yr) 1628 1153 

Reduction Factor (see Table 5) 51% 65% 

Load Reduction Goal (kg/yr) 830 749 

Mercury Load Allocation (kg/d) 2.18 1.10 

Regional Area (km2

) 129,674 90,151 

Mercury Deposition Goal (g km-2 yr-1) 6.1 4.4 

Up to this point no assumptions are made about where the mercury reductions will come from, although it 

is clear from the estimate of total source load that the reductions must come from atmospheric deposition. 

If we therefore assume all mercury reductions must come from atmospheric deposition, dividing the 

mercury loading goal by the regional areas gives the areal mercury deposition goals of 4.4 g km-2 yr-1 for 

the NE region and 6.1 g km-2 yr-1 for the SW region. 

4.4

NE

6.1

SW

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2.5 5 7.5 10 12.5 15

Atmos. Hg Deposition (g km-2 yr

-1)

90th Percentile Fish Hg (mg/kg)

1990 

GOAL 

Figure 18 Proportional relationship between mercury deposition and fish mercury concentration 

in the two TMDL regions 

MN Statewide Mercury TMDL 27MAR07_final.doc 38
The reductions in fish mercury concentrations (90th percentile) in proportion to atmospheric mercury 

deposition are illustrated for each region in Figure 18. Atmospheric mercury deposition in 1990 was 12.5 

g km-2 yr-1 for both the NE and SW regions; while the 90th percentile mercury concentrations for standard 

size walleye were 0.572 mg/kg in the NE region and 0.405 mg/kg in the SW region. As discussed in 

Section 5.2, mercury concentrations in the fish are expected to eventually decrease in proportion to the 

decrease in atmospheric mercury deposition. The lines connecting the 1990 fish mercury concentrations 

to the graph’s origin represent the proportional decrease. The ultimate goal is to achieve 0.2 mg/kg fish 

mercury level in both the NE and SW, which requires a 65% decrease in the NE and a 51% decrease in 

the SW. Assuming the mercury deposition continues to be uniform across the state, the NE will not meet 

its goal when the SW has met its goal; therefore, the lower mercury deposition goal of 4.4 g km-2 yr-1

becomes the necessary goal for the whole state. 

As described in Section 5, atmospheric sources of mercury in Minnesota are categorized as 70% 

anthropogenic and 30% natural. Natural sources cannot be controlled and are expected to remain at the 

same long term average; therefore, all mercury reductions must come from anthropogenic sources. 

Taking load reductions from anthropogenic sources results in a 93% reduction for the NE and 73% 

reduction for the SW (Table 9). State sources are 10% of all mercury deposition (0.25 • 40% regional 

sources) and 14% of the anthropogenic sources (10% ÷ 70% = 0.143). 

Table 9 Mercury Load Allocation for In-State and Out-of-State Emissions 

TMDL Region 

SW NE 

Load reduction from anthropogenic sources 

 (RF ÷ 0.7) 73% 93% 

State’s fraction of anthropogenic sources (10% ÷ 70%) 0.143 0.143 

In-State contribution to the TMDL Load Allocation 

(0.143 • LA) 

0.31 kg/d 

(249 lb/y) 

0.16 kg/d 

(126 lb/y) 

Out-of-State contribution to the TMDL Load Allocation 

[(1- 0.143) • LA] 

1.86 kg/d 

(1,495 lb/y) 

0.94 kg/d 

(756 lb/y) 

Consequently, the in-state load allocations of the TMDL are 0.31 kg/d and 0.16 kg/d for the SW and 

NE regions. The remaining load reductions must come from outside the state and are, therefore, 

the out-of-state load allocations. 

The state’s load reduction goals can be translated to emission reduction goals based on the 1990 baseline 

year emissions and deposition. Atmospheric deposition of mercury is considered uniform across the 

state, and emissions dispersion within the state overlaps the two regions; therefore, the greater regional 

reduction goal must be applied to a statewide emissions goal to achieve the goal in the more sensitive 

region.3

 Total mercury emissions in Minnesota were estimated to be 5113 kg in 1990. A 65% reduction 

in total deposition translates to a 93% reduction of anthropogenic deposition. The state’s contribution to 

emissions must be reduced 93%, along with other anthropogenic sources to meet the 65% reduction in 

total deposition (Table 10). The state’s emissions must be reduced from 11,272 lb (5113 kg) in 1990 to 

789 lb (358 kg) as a final annual emissions goal (Table 10). 

 

3

 This approach is consistent with the accepted approach to environmental protection; for example, dissolved oxygen 

(DO) water quality standards are applied at a point in a receiving water where the DO concentration is lowest (the 

“DO Sag”) or to the early morning hours when DO is lowest within a diurnal cycle. 

MN Statewide Mercury TMDL 27MAR07_final.doc 39
Table 10 Minnesota’s Mercury TMDL Emissions Reduction Goal 

Annual Statewide 

Mercury Emissions 

State mercury emissions for 1990 11,272 lb (5,113 kg) 

Mercury Emissions Reduction Goal (0.93 • 1990 emissions) 10,483 lb (4,755 kg) 

Mercury Emissions Goal (1990 Emissions – Reduction Goal) 789 lb (358 kg) 

Emissions reduction as of 2005 (70% of 1990 emissions) 7,931 lb (3,597 kg) 

Emissions reduction remaining as of 2005 to achieve goal 2,552 lb (1,158 kg) 

Percent of 1990 Emissions Reduction Goal remaining as of 2005 24% 

Based on the mercury emissions inventory for 2005, 76% of this emissions reduction goal has been 

achieved; therefore, as of 2005, 24% of the reduction goal remains. 

6.5 Reserve Capacity 

Reserve capacity refers to load that is available for future growth when actual loads are less than the load 

allocation. There is no reserve capacity for nonpoint sources, because actual nonpoint source loads are far 

in excess of the Load Allocation. Reserve capacity is available for water point sources, because the actual 

mercury load is less than the Wasteload Allocation. The wasteload allocation for this mercury TMDL is 

set at one percent of the TMDL or equal to the 1990 point source load, whichever is lower. The one 

percent level is 4 kg for the NE region and 8 kg for the SW. The 1990 point source load in the SW was 7 

kg; therefore, the wasteload allocation is set at 7 kg rather than 8 kg. One percent is considered a de 

minimus level, meaning mercury load at, or below, this level is insignificant. Therefore, any changes in 

load below the de minimus level are insignificant. The estimated mercury point source load in 2004 was 

about 7 kg for the state, resulting is a reserve capacity of about 4 kg. The mercury TMDL 

implementation plan will establish a procedure to account for the reserve capacity potentially available for 

new and expanded sources. 

7 Margin of Safety 

A Margin of Safety (MOS) is required in the TMDL to account for uncertainty in the TMDL calculations. 

MOS can be either explicit (e.g., additional 10% load reduction), implicit in the calculations, or a mix of 

the two. In conventional TMDLs, uncertainty arises through the use of water quality models and Best 

Management Practice (BMP) choices. An implicit MOS can include using the most conservative 

parameters when there is a range from which to choose or using the most conservative effectiveness 

assumption when selecting BMPs. In this mercury TMDL, uncertainty arises from the mercury 

movement through the environment, and, in particular, the conversion of inorganic mercury to 

methylmercury. Very important, but still poorly understood, are the sulfate-reducing bacteria, which 

methylate the mercury and are abundant in wetlands. 

The greater abundance of wetlands in the NE region and the associated sulfate-reducing bacteria is 

thought to be one of the major reasons why fish mercury concentrations are significantly higher than in 

the SW region. Research by the Agency and others are actively pursuing this important link between 

sulfate reduction and fish tissue methylmercury levels. Lowering sulfate load to wetlands could reduce 

MN Statewide Mercury TMDL 27MAR07_final.doc 40
the sulfate-reducing bacteria activity and thereby reduce the methylation of inorganic mercury. 

Consequently, the needed mercury load reduction would have to be less. 

We know sources of atmospheric sulfate are actively being reduced through a variety of activities at the 

federal and state levels. We believe the reduction in fish mercury through reductions in sulfate could be 

significant. The Agency believes the relationship between sulfate concentrations and methylmercury 

concentrations is adequately established, but not to the degree that we can determine an explicit MOS. 

Thus, for this initial phase of the TMDL, it will be the primary implicit MOS for the NE region. 

The SW region has an explicit MOS, because the TMDL goal is a statewide 93% reduction in mercury 

emissions. This is protective of the NE region but over-protects for the SW region, which has only a 73% 

mercury emission reduction goal. Uniform deposition across the entire state is the reason for the more 

protective requirement in the SW region. 

8 Seasonal Variation and Critical Conditions 

Seasonal variations and “... critical conditions for stream flow, loading, and water quality parameters” are 

discussed in 40 CFR 130.7(c)(1). Fish accumulate enough mercury over the years of their lifespan to 

become a health hazard to humans and wildlife. Mercury deposition and water concentrations fluctuate 

based on seasonal rainfall patterns; however, seasonal variations are not significant to this TMDL because 

it is expressed as an average annual load. The mercury concentration in the fish represents an integration 

of all temporal variation up to the time of sample collection. Variability among fish because of 

differences in size, diet, habitat, and other undefined factors are expected to be greater in sum than 

seasonal variability. 

Critical conditions, such as dawn period for low dissolved oxygen, are not relevant to mercury in fish 

because the fish tissue concentrations reflect integration over time of various factors. However, there are 

critical conditions in the sense of water bodies that are more sensitive to mercury loading because of their 

water chemistry. This aspect of critical conditions has been addressed in this TMDL by using the 

regional approach and acknowledging that the NE region is more sensitive to mercury loading than the 

SW region. 

9 Final TMDL 

The conventional equation for a TMDL is as follows: TMDL = WLA + LA + MOS. As described above, 

the Margin of Safety (MOS) is implicit for the NE region and, therefore, not quantifiable. The MOS for 

the SW region was given in terms of the anthropogenic emissions reduction goal (i.e., 93% reduction 

matching the NE, rather than 73%). If the MOS for the SW were interpreted as applying the NE 

Reduction Factor of 65%, instead of 51%, the LA for the SW is reduced from 2.16 kg/d to 1.55 kg/d, 

which leaves a MOS of 0.62 kg/d. The NE and SW regional TMDLs fit the TMDL equation as follows: 

NE Region TMDL (1.10 kg/d) = WLA (0.01 kg/d) + LA (1.09 kg/d) + MOS (implicit) (11) 

SW Region TMDL (2.18 kg/d) = WLA (0.02 kg/d) + LA (1.55 kg/d) + MOS (0.61 kg/d) (12) 

The WLA is defined for these mercury TMDLs as one percent of the TMDL to ensure that water point 

source mercury load remains de minimus. 

As required by Federal law, this TMDL is not applicable to waters in Indian Country. 

MN Statewide Mercury TMDL 27MAR07_final.doc 41
10 Monitoring & Research Plan 

Monitoring to detect environmental change to changing atmospheric mercury deposition will follow the 

recommendations of Mason et al. (2004). Monitoring options that are being considered include the 

following: 

• Fish contaminant monitoring of previously sampled lakes and rivers (this is ongoing) 

• Sentinel lakes: 4-5 lakes around each of the MDN sites in Minnesota; monitor air, water, & fish 

tissue (biopsy) 

• Lake sediment cores and recalculation of mercury deposition for representative lakes 

• NPDES upstream/downstream monitoring for traditional wasteload allocation studies 

• Continued air monitoring for wet deposition; new monitoring stations required for dry deposition 

and urban areas 

The MPCA and its research partners in Minnesota are studying factors affecting mercury contamination 

of fish. Widely cited Minnesota research in the 1990s analyzed lake sediment cores to estimate historical 

mercury deposition and its sources. Current work is focused on understanding the local factors, such as 

land cover effects and food chain structure, which might explain the observed variability in mercury 

bioaccumulation among lakes. Another research project in the state is testing the effect of increased 

sulfate deposition on mercury methylation in a wetland (Jeremiason et al. 2003). The outcomes of these 

studies will help refine the implementation of the mercury TMDLs. 

11 Projected Implementation 

11.1 Background 

According to USEPA’s Guidance for Water Quality-based Decisions: The TMDL Process (EPA 440/4-

91-001), TMDL development activities consist of the following process – selection of the pollutant to 

consider, estimation of the waterbody’s assimilative capacity, estimation of the pollution from all sources 

to the waterbody, determination of total allowable load, and, finally, allocation (with a margin of safety) 

of pollution reductions such that water quality standards are met. This has been accomplished in the 

preceding sections. 

Implementation planning is not a formal requirement of the TMDL process. This is very clear in Figure 2 

on page 21 of the 1991 TMDL Guidance document noted above – detailed implementation planning 

occurs after the TMDL plan is approved by USEPA. The Clean Water Act describes implementation 

planning in the section following TMDL requirements, Section 303(e). However, it is has long been 

recognized that the TMDL planning document should contain at least the outline of the specific 

implementation planning needed to meet the pollution reduction goals set in the TMDL. This informs the 

public and aids in the discussion on reasonable assurance. 

Once this TMDL pollution reduction plan is approved by USEPA, the reduction goals are legally 

enforceable to the extent that legal authorities exist. This TMDL will not generate new legal authorities. 

Draft implementation planning is not legally enforceable – they are approaches that the Agency believes 

are appropriate, but subject to change based on further refinement as the implementation planning 

becomes more developed. 

11.2 General Approach 

The best available information was used to establish this TMDL; nevertheless, uncertainty warrants an 

adaptive watershed management approach to implementation (Dilks and Freedman 2004). The TMDL 

MN Statewide Mercury TMDL 27MAR07_final.doc 42
implementation will incorporate the adaptive watershed management approach by establishing a 

monitoring plan, interim targets, and a timeline. Future information and analysis may warrant revisions 

in the goals or the tools used to assess progress toward the goals. 

An important component in developing a strategy to meet water-quality standards is to consider the value 

and effectiveness of efforts already in place. As noted previously, from 1990 to the present Minnesota’s 

mercury emissions were reduced more than 70%. This section summarizes initiatives that the MPCA 

believes have already reduced fish contamination in Minnesota and will maintain a path of reduced fish 

contamination in the future. In addition to reductions from Minnesota sources, reductions in air emissions 

of mercury by national and international sources will be needed to meet Clean Water Act standards in 

Minnesota, because there is significant mercury deposition in Minnesota from these sources. 

Reduced deposition of mercury is projected to have beneficial human-health and environmental effects, 

which produce economic benefits. To estimate the total economic value of improvements in 

environmental goods and services, a state-wide contingent-valuation study was completed in 1999 (Hagen 

et al. 1999). The study was designed to elicit the willingness of Minnesota households to pay for 

reductions in adverse health and environmental effects that result from mercury deposition. A major 

conclusion was a best estimate annual state willingness to pay of $212 million for a policy that was 

projected to reduce mercury deposition in Minnesota by approximately 12%. The willingness to pay was 

greater for greater reductions in mercury deposition; therefore, it follows that the reductions outlined in 

this TMDL report (i.e., 65% reduction in mercury deposition) would translate to a much greater economic 

benefit within the state. These reductions will also significantly reduce health risks associated with 

ingesting fish containing excess mercury. 

11.3 Implementation for Wasteload Allocation 

Despite the relatively very minor contribution of point sources to the total mercury load, the Agency will 

continue to strive to reduce mercury from all sources inside the state, including point source water 

discharges. To do so, the permitted facilities will establish mercury minimization plans (Table 11). In 

receiving water segments that are discharge-dominated, the dischargers will be subject to permit 

conditions that address ambient fish tissue monitoring. This monitoring will determine the relationship of 

the de minimus assumption with actual fish tissue conditions on a more localized basis and could result in 

mercury limitations in NPDES permits. 

Table 11 WWTP Mercury Reduction Plan 

WWTP Average Wet 

Weather Flow (g/d) 

Sampling 

per Year 

Mercury Minimization 

Plan (MMP) Required 

Less than 200,000 0 NO 

200,000 – 500,000 1 YES 

Greater than 500,000 4 YES 

The sum of municipal WWTP, stormwater & industrial WWTP WLA loads shall remain de minimus, i.e. 

less than 1% of the atmospheric deposition load or 11 kg per year. This includes both existing WLA 

facilities, expanding facilities, and new facilities. MMPs and monitoring will be required for those 

facilities with a wet weather design flow of 0.2 mgd or greater. MMPs will include minimization of 

mercury in solids as well as in discharge. 

Additional restrictions will be required if the de minimus is exceeded. For new/growth permits in the SW 

region, the focus will be trading, either with [1] NPS sediment reductions (the ratio must be agreed upon), 

[2] stormwater sediment reductions in the areas that are growing (the ratio must be agreed upon), and/or 

[3] trade-up in treatment to Bio-P or Chem-P, either of which will reduce the effluent mercury to below 

the new WQS after out-of-state reduction goals are met. Bio-P seems to reduce mercury to about one-half 

to one-third of the previous average effluent concentration. 

MN Statewide Mercury TMDL 27MAR07_final.doc 43
For the NE region, new/growth permits will focus on trading, either with [1] air sources for sulfur 

reductions and/or mercury reductions, [2] stormwater sediment reductions, and/or [3] inflow/infiltration 

(I/I) reductions. Bio-P is also an important option. 

The exception to the de minimus provisions for the WLA portion of this TMDL originates with the water 

quality rules for the Lake Superior Basin, Chapter 7052, and the GLI Guidance from which it was 

derived. Provisions for the phase-out of mixing zones for existing dischargers by March 23, 2007, and 

for not allowing mixing zones for new or expanded dischargers at commencement of discharge are 

specific to GLI and Chapter 7052. These provisions apply when establishing a TMDL. Therefore, all 

dischargers in the Basin will initially or eventually need to meet the 1.3 ng/l mercury water quality 

standard and mass caps as a waste load allocation for their discharge. 

11.4 Implementation for Load Allocation 

Minnesota clearly is dependent upon other areas to reduce emissions, and Minnesota has set an example 

that other areas should emulate. Minnesota has, through both voluntary and regulatory approaches, 

reduced mercury emissions by 68% between 1990 and 2000 (See section 5.3.1), and the MPCA expects to 

meet the mandated reduction goal of 70% by 2005. (The 68% reduction of the 1990 mercury emissions is 

equal to 73% of the mercury TMDL reduction goal.) Mercury reductions outside the State have not been 

quantified, although USEPA reports national emissions have been reduced at least 45% between 1990 and 

1999 (See section 5.3.1). 

Attempting to reduce Minnesota’s fish contamination by exporting more of our emissions—through 

higher stacks or intentional conversion of divalent mercury emissions to elemental mercury—invites other 

areas to also export mercury, which probably would result in greater fish contamination in Minnesota. 

Therefore, Minnesota’s mercury TMDL emission reduction strategy is to calculate the percent reduction 

that is needed and reduce mercury emissions by that degree without regard for where the emissions will 

be deposited. 

To maintain economic fairness while focusing on meeting water quality standards, the Agency will 

employ a phased approach to achieve a goal of 789 pounds of mercury emitted from all Minnesota 

sources. Short-term actions, check-in points, and future action options are described below. The sectorspecific reduction milestones will be used as guideposts by the MPCA to decide whether reductions are 

on track in the future. If emission reductions are not on track, the MPCA will review the current state of 

knowledge about mercury deposition and control options and costs, and develop a strategy to obtain 

further reductions to achieve the milestone. The strategy will contain regulatory controls as necessary to 

reach target goals. 

Recognizing the overall goal of reducing mercury deposition in the state, one sector might reduce more 

than the sector goal, while another sector is not able to reduce as much, yet the reduction strategy may 

still achieve its goal. The same is true for the ratio of in-state to out-of-state reductions. If national, 

international, and other state reductions are large enough, those reductions may obviate the need for some 

reductions in Minnesota. This is important because over the past decade Minnesota has reduced mercury 

emissions using cost-effective steps that others may not yet have taken. 

Section 12 outlines the mercury reduction programs underway in Minnesota, nationally, and 

internationally. It provides the assurance that several robust mercury control programs are wellestablished and have been very effective. Section 5 provides context that fish tissue concentrations have 

been in decline in recent years, mercury emissions are trending down in all relevant emission inventories, 

and that reduced sulfate concentrations from sulfur dioxide emission reduction programs may magnify the 

benefit of reduced mercury emissions. 

After finalizing and submitting this TMDL to USEPA for approval, the MPCA will begin to work with 

stakeholders to develop an implementation plan. As explained above, the implementation plan is not a 

MN Statewide Mercury TMDL 27MAR07_final.doc 44
formal requirement of the TMDL process. The TMDL is expected to contain an outline of the specific 

implementation planning needed to meet the TMDL goal. The MPCA expects to conduct in-depth 

implementation planning in 2005-2006 after this TMDL is approved. The implementation planning 

process will need to involve a careful review of the cost and efficacy of technically available control 

options, and the development of federal regulations that would reduce mercury emissions from source 

categories like power plants, mini-mills and industrial boilers. 

11.4.1 Short-term Actions 

New and Expanding Sources of Mercury to the Atmosphere 

To limit growth of mercury emissions because of construction of new or expanding emission sources in 

Minnesota, the MPCA will develop a permitting strategy for new and/or expanding air emissions sources 

of mercury that considers the following: 

• Establishing an appropriate facility de minimus emissions rate 

• Requiring new or expanding sources to use state-of-the-art mercury control technology if the de 

minimus rate is not feasible/achievable/possible 

• Investigating how to allow offsetting reductions 

Develop Monitoring and Reporting Protocol 

The MPCA will work with air emission sources to develop a monitoring and reporting protocol with the 

goal of better quantifying annual mercury emissions. An improved Minnesota air emissions inventory is 

needed to track progress at meeting reduction targets. 

Current Reduction Strategies 

The MPCA will continue to employ strategies already in place as described below to continue the trend of 

decreased air emissions. The MPCA expects interim and final targets will be met, especially considering 

pending federal regulations and a strong commitment to voluntary reductions by existing facilities. 

Continue existing state regulations and programs to collect mercury. Existing regulations, including 

product bans, disposal requirements and pollution control equipment at waste combustors will continue to 

reduce product-sector emissions. Additionally, the MPCA and the Minnesota Office of Environmental 

Assistance continues to identify and provide education to industrial sectors and Minnesota citizens about 

proper storage and management of mercury-bearing wastes. 

Support voluntary reductions. Under the MPCA’s current mercury strategy, the MPCA expects 

facilities to voluntarily reduce air emissions whenever possible. The MPCA will continue to work with 

air emission sources to encourage reductions. 

Encourage the development of federal regulations: MPCA believes that a national program regulating 

mercury emissions from existing and future emission sources holds the most promise, by addressing the 

substantial contribution by sources outside of Minnesota to Minnesota water bodies while minimizing 

competitive disadvantages that a state-level only regulation could create. The MPCA will continue to 

work with EPA to implement control standards/programs that require substantial reductions from electric 

utilities, steel mini-mills, crematories and other emissions sources across the country. The MPCA filed 

detailed comments with USEPA in 2004 urging promulgation of strong federal mercury reduction 

requirements for the electric power sector. 

Evaluate impacts of federal regulations. The MPCA will continue to assess the impacts of federal 

actions to inform potential additional state regulatory actions. In particular, the MPCA will closely 

follow the development and implementation of the federal mercury emission reduction program for power 

MN Statewide Mercury TMDL 27MAR07_final.doc 45
plants: the Clean Air Mercury Rule. The Implementation Plan will thus be able to consider the effect of 

that standard on power plant emissions. At the same time, USEPA is finalizing a new regulation that 

would reduce sulfur dioxide emissions in the eastern US by 70%. MPCA will continue to investigate 

whether sulfur dioxide reductions of this scale will magnify the effect of mercury emission reductions, 

and the impact of the program on Minnesota’s reduction targets. 

Investigate regional state cooperation. In the absence of strong federal regulations, reductions in 

Minnesota may be more effectively and equitably achieved by cooperating with other states in the region 

to develop strategies to reduce emissions sources. The MPCA will actively coordinate the above 

strategies and consider regional regulations if needed to meet reduction targets. 

11.4.2 Reduction Targets and Milestones 

Substantial reductions are necessary from existing sources to achieve a 93% reduction in overall 

anthropogenic emissions from 1990 levels. To initiate development of an implementation plan, the 

MPCA has set overall and sector-specific reduction targets (Table 12) for the in-state energy, taconite and 

products sectors with interim outcome-based targets. These targets will guide the MPCA in its 

implementation planning. They will aid in establishing set intervals for the MPCA to evaluate progress, 

reviewing recent developments in controlling mercury emissions, and assessing on new strategies. 

An example of ways that future federal regulations might affect Minnesota’s goals is the proposed 

mercury cap and trade program. Mercury emission control on power plants is expensive, and becomes 

more expensive as the reduction target moves from 70% to 80% to 90%. The Acid Rain program of the 

1990 Clean Air Act Amendments showed that a cap and trade program is extremely cost-effective in 

meeting emission reduction targets because it drives reductions to the place where larger, cheaper 

reductions can be made. The USEPA has adopted a cap and trade program as the basis for the Clean Air 

Mercury Rule (issued March 15, 2005). In the Mercury TMDL implementation plan, the MPCA will 

consider the appropriateness of keeping a state sector target if the national trading program will assure 

that the national power sector will reach an adequate percentage reduction in mercury emissions. 

Table 12 Summary of Reduction Targets 

Sector 

1990 

Emissions 

2000 

Emissions Target #1 Target #2 Target #3 

Energy 1,667 1,834 675 470 313 

Material Processing 723 758 550 280 138 

Products 8,881 1,045 475 350 338 

All sources 11,272 3,638 1,700 1,100 789 

For Target #1, when the national emission reductions are expected to reach 65% from 1990, the state 

target of 1700 pounds [Target #1] must be reached. If the state target is not met, regulatory tools will be 

developed as necessary to reach target goals, unless achieved national reductions exceed their target and 

obviate the need for some of the state reductions. 

For Target #2, when the national emission reductions are expected to reach 80% from 1990, the state 

target of 1100 pounds [Target #2] must be reached. If the state target is not met, regulatory tools will be 

developed as necessary to reach target goals, unless achieved national reductions exceed their target and 

obviate the need for some of the state reductions. 

For Target #3, when the national emission reductions are expected to reach 93% from 1990, the state 

target of 789 pounds [Target #3] must be reached. If the state target is not met, regulatory tools will be 

developed as necessary to reach target goals, unless achieved national reductions exceed their target and 

obviate the need for some of the state reductions. 

MN Statewide Mercury TMDL 27MAR07_final.doc 46
11.4.3 Regulatory Actions 

The MPCA has identified potential regulatory options for ensuring reasonable progress towards achieving 

the targets of the TMDL, some of which were selected from the 1999 Mercury Contamination Reduction 

Initiative Advisory Council’s Source Reduction Feasibility and Reduction Strategies (SRFRS) Committee 

Report on Options & Strategies for Reducing Mercury Releases4

. If current reduction strategies, 

including upcoming federal regulations and voluntary measures, under-achieve by not reaching interim or 

final target goals, the agency will need to consider further voluntary strategies and enact regulatory 

approaches to meet TMDL reduction requirements to ensure that the final reduction target are reached. 

These strategies might include: 

• Technology-based limits for emissions sources 

• Establish a sector-level cap 

• Establish a state-level cap and trade system 

• Impose fees on mercury emissions 

12 Reasonable Assurance 

12.1Assurances Occur at Multiple Levels 

A complete TMDL evaluation requires reasonable assurance that the impaired waters will attain water 

quality standards. When water point sources dominate as pollutant sources, reasonable assurance is 

straightforward: implement reduction in NPDES permits. This is not the case when nonpoint sources are 

the major source of the pollutant. For this Minnesota Mercury TMDL, there are reasonable assurances in 

the past actions on state, federal, and international levels that had a measurable affect on sources of 

mercury. Can we also see a measurable affect on environmental concentrations of mercury, and 

especially on the endpoint: mercury in fish? The first subsection below summarizes what reasonable 

assurances we can determine from research and monitoring of mercury in the environment. Other aspects 

of reasonable assurance are present and future decisions: 

will actions to reduce mercury contamination continue, 

and what new or proposed actions will reduce mercury? 

Subsections below summarize what we consider positive 

steps to reduce mercury on the three governmental levels. 

12.2 State Level Assurances 

Minnesota has been a national leader in reducing mercury 

releases to the air, water and land since the early 1990s. 

The state employs an array of voluntary, regulatory, 

incentive-based and educational tools that involve local 

governments, state agencies and businesses. In concert 

with similar initiatives on the Federal level, Minnesota’s 

efforts have contributed to a 70% reduction in mercury 

emissions over the last 13 years (Table 13). The Minnesota Mercury Emissions Inventory (MPCA 2005) 

describes the specific statewide mercury emissions in 1990, 1995, and 2000. The MPCA mercury 

emission inventory has an earlier baseline and is more inclusive than the USEPA inventory. The USEPA 

inventory tends to exclude sources that are more difficult to quantify or verify. The best example of such 

a source is the large amounts of mercury that must have volatilized from latex paint until it was no longer 

added to paint after 1992. 

Carol Hubbard and Clancy inspecting a 

classroom for mercury 

 

4

 MPCA, 1999. available at http://www.pca.state.mn.us/air/mercury-mn.html#initiative 

MN Statewide Mercury TMDL 27MAR07_final.doc 47
Table 13 Summary of Mercury Reduction Strategies Used in Minnesota Since 1990 

Voluntary Programs

Health Care Outreach Education on management & reduction of mercury-containing equipment. 

Household/Small 

Business Hazardous 

Waste Collection 

Many county-run programs accept mercury-containing items from 

homeowners and businesses. 

Dental Office Outreach Municipal wastewater treatment plants and the Minn. Dental Assoc. 

established best management practices and goals for 100% participation. 

Thermostat Take-back Through a reverse distribution system involving contractors and wholesalers, 

manufacturers take back out-of-service units. 

Mercury Switches in 

Automobiles 

Law requires “good faith effort” to remove mercury switches prior to crushing; 

bounty of $1/switch offered by major steel recycler. 

Mercury-Free Zone 

Program 

Schools pledge to be mercury free and receive an assessment and 

educational visit by the MPCA’s mercury educator, Carol Hubbard, and 

Clancy, its mercury-detecting dog. 

Voluntary Reduction 

Agreements 

Large emitters enter into voluntary agreements to reduce emissions. 

http://www.pca.state.mn.us/air/mercury-mn.html 

Regulatory Programs 

Waste Combustor 

Standards 

Sets air emission limits on mercury and requires mercury reduction plans for 

municipal and medical waste incinerators. 

Water Discharge 

Standards 

Waste water dischargers are required to monitor for mercury using EPA 

Method 1631; mercury effluent limits are set in some cases 

State Laws 

Fluorescent Lamp, 

Other Product Disposal 

Ban 

Requires businesses and households to recycle fluorescent lamps, 

stimulating development of recycling infrastructure. 

Mercury-containing 

Product Bans 

Toys, games, apparel and thermometers that contain mercury may not be 

sold in Minnesota 

Dairy Manometer Ban 

and Buy-back 

Bans the sale, installation and repair of mercury-containing manometers, 

establishes $100 incentive for turning in old gauge. 

Relay Manufacturer 

Responsibility 

Requires manufactures of mercury displacement relays to provide education 

and incentives, cover costs of managing out-of-service units. 

Battery Mercury 

Reduction 

Bans mercuric oxide batteries and the addition of Hg to alkaline batteries. 

Establishes a 25-mg limit in button batteries. 

Mercury in 

Construction/Demolition 

Law prohibits disposal, implying removal prior to demolition. Education and 

enforcement conducted. 

Mercury Reduction Law 

(1999) 

Requires the state to pursue Advisory-Council-recommended strategies, 

establishes a goal of 70% reduction in emissions by 2005 based on 1990 

levels. Final report due in 2005. 

Many of Minnesota’s mercury-reduction initiatives have become national models. For example, the 

thermostat industry’s voluntary take-back program for mercury thermostats started as a collaborative pilot 

in Minnesota and is now a nationwide program. The Minnesota Legislature passed some of the first laws 

in the country banning mercury in certain products, some of which (e.g., zero mercury in alkaline 

batteries) led to similar national laws. 

Minnesota also adopted rules setting standards for municipal and medical waste incinerators ahead of 

federal requirements that call for stricter emissions limits than the current federal standard. These waste 

combustor standards, coupled with increased mercury product management and reduction, led to a 93% 

MN Statewide Mercury TMDL 27MAR07_final.doc 48
decrease in emissions from municipal and medical waste incinerators, dropping from 1,053 kg (2,322 lb) 

in 1990 to 76 kg (167 lb) in 2000.5

In 1996, the MPCA initiated the Mercury Contamination Reduction Initiative aimed at reducing mercury 

contamination of fish in Minnesota lakes and rivers. As part of the initiative, the agency formed a 

stakeholder advisory council to develop recommendations on mercury-reduction strategies. The advisory 

council’s recommendations were adopted by the Minnesota Legislature in 1999 and continue to form the 

basis of Minnesota’s mercury-reduction program. These strategies include establishing reduction goals, 

national and international strategies, research, reducing purposeful use, and voluntary agreements. 

Minnesota’s statewide mercury-reduction goal, recommended by the advisory council and set in state 

statute, is to reduce annual mercury releases 60% by 2000 and 70% by 2005, compared to 1990 levels. 

The MPCA estimates statewide emissions in 2000 of 1,650 kg (3,638 lb), a 68% reduction from estimated 

1990 levels. Minnesota mercury emissions sources and trends are discussed in more detail in 

Section 5.3.1. 

The 1999 law established a voluntary mercury-reduction agreement program encouraging the largest 

emitters in the state to enter into agreements with the MPCA to voluntarily reduce their mercury air 

emissions. Participants in the program are expected to implement cost-effective, technologically feasible 

reduction measures. The MPCA agreed not to pursue additional state regulations, at least until 2005, as 

long as adequate progress is made in reducing emissions (MPCA 2002). 

Twelve companies and two regional waste management jurisdictions participate in the voluntary 

agreement program and have implemented steps to reduce emissions, pledged reductions or engaged in 

research in the hope of discovering future reduction strategies. Progress reports are available at 

http://www.pca.state.mn.us/air/mercury-mn.html. When fully implemented, reduction agreement actions 

initiated to date will result in additional reduction in annual emissions of an estimated 155 kg (342 lb) by 

2008, or about 9.4% of 2000 emissions. These actions include fuel switching and increased controls by 

electric utilities [a 120 kg (264 lb) annual decrease, or 16% reduction for the sector] and added controls 

on sewage-sludge incineration [35 kg (78 lb) or 70% sector reduction]. In addition, participants have 

removed from their plants and properly managed hundreds of pounds of mercury-containing equipment, 

mercury that could have been released to the environment. 

Minnesota continues to work with stakeholders to reduce mercury releases to the environment from 

product-related uses, taconite processing and energy production. Continued reductions in product-related 

emissions are expected as mercury use in products declines and sound management increases. However, 

achieving significant reductions beyond the progress to date will require reductions in mercury emissions 

in the taconite and power-generation sectors. Currently, no cost-effective reduction technologies have 

been identified for taconite-processing operations. The MPCA and the Minnesota Department of Natural 

Resources are working with Minnesota’s taconite industry to identify future control technologies and 

funding research to develop these technologies. 

In 2000, as part of a commitment to reduce emissions under the state’s voluntary mercury-reduction 

agreements, Minnesota Power substituted lower-mercury coal to achieve a 32 kg (70 lb) annual reduction 

in mercury emissions from its operations. 

In December 2003, the Public Utilities Commission approved Xcel Energy’s Metropolitan Emissions 

Reduction Program (MERP) that will re-fire two coal plants with natural gas and upgrade the pollutioncontrol equipment at a third, metro-area plant. When fully implemented in 2009, the MERP will result in 

an estimated annual mercury reduction of 77 kg (170 lb). 

 

5

 Changes in mercury emissions after 1990 are not included in the TMDL calculation, since the TMDL is based on 

the 1990 baseline year. 

MN Statewide Mercury TMDL 27MAR07_final.doc 49
Taken together, Minnesota Power’s lower-mercury coal and Xcels’ MERP will result in a reduction of 

109 kg (240 lb), a 16% reduction in utility-sector emissions and a 6.3% reduction in total emissions 

compared to 2000 levels. These reductions will account for a 2% reduction in total emissions when fully 

implemented (based on 1990 levels). The MPCA is awaiting the outcome of Clean Air Act standards 

development for power plants and several multi-pollutant proposals in Congress that have the potential to 

significantly decrease mercury emissions from power generation. 

Metropolitan Council Environmental Services (MCES) operates two sewage sludge incinerators. 

Mercury emissions from these plants dropped from 112 kg (247 lb) in 1990 to 51 kg (112 lb) by 2000 

largely because of reducing mercury inputs to the wastewater. The MCES is constructing a new sewage 

sludge incinerator at its metro plant (scheduled to go on line in mid-2004) and expects mercury emissions 

to be reduced by approximately 35 kg (78 lb). 

MPCA will propose for rulemaking that new or expanding dischargers get 1 mg/L limit for total 

phosphorus if they discharge more than 1800 lbs phosphorus per year. The new limit will result in more 

facilities adding Bio-P or Chem-P processes to reduce phosphorus; these processes have already been 

added to a number of large WWTP in Minnesota and data collection has shown reductions in mercury 

concentrations as well, by one-half to two-thirds. Therefore, continued mercury reductions from WWTPs 

are expected as the 1 mg/L phosphorus limit is implemented. 

12.3 National and International Assurances 

Because of long-range transport of mercury in the atmosphere, reductions in mercury air emissions 

outside of Minnesota will eventually lead to reduced mercury deposition in Minnesota and reduced 

contamination of Minnesota fish. A variety of programs, initiatives and regulations exist in North 

America and internationally to reduce mercury emissions (Table 14). Notably in 2003, the United 

Nations Environmental Programme determined that mercury is a Pollutant of Concern that warrants 

international action and established a mercury program to assist developing countries with identification 

and reduction of mercury emissions. Given these programs, the success of mercury-reduction initiatives 

in developed countries and the eventual transfer of technology to the developing world, the MPCA 

expects that these initiatives will eventually lead to reductions sufficient to reduce fish mercury 

concentrations in Minnesota water bodies. However, uncertainties about the timing of implementation of 

reduction efforts world-wide and the complexity of mercury cycling make it difficult to predict when the 

effects of these actions will result in significant improvements in Minnesota. 

Minnesota participates, where it can, in these national and international mercury reduction initiatives. 

Minnesota has been involved to a certain extent in all the national and regional initiatives listed in Table 

14, as well as some international activities. 

Mercury emissions from coal combustion in the United States are expected to decline because of 

technological innovation under the MACT or the Clear Skies Initiative, and that cost-effective mercury 

control will be adopted world wide following its development in the United States. These additional 

emissions reductions are expected to result in additional reductions in mercury contamination of fish after 

a dynamic equilibrium is reached. 

MN Statewide Mercury TMDL 27MAR07_final.doc 50
Table 14 Summary of Regional, National and International Mercury Reduction Initiatives 

Program Description Comments 

Regional Initiatives

Lake Superior Programs Binational Program, LAMP Virtual elimination by 2020 

Great Lakes Binational Toxics Strategy 50% reduction by 2006 

St. Louis River (northern 

Minnesota) 

Area of Concern Remedial Action 

Plan 

National Initiatives

EPA’s Proposed Rules 

for Coal-fired power 

plants - 2004 

CAAA Section 112 Maximum 

Achievable Control Technology 

standard or Section 111 standards 

68% reduction in current emissions 

by 2018 under Section 111 standards 

(15 ton emissions cap) 

Mercury Legislative 

Proposals — Coal-fired 

Utility 

Various proposals currently before 

Congress including the President’s 

“Clear Skies Initiative” 

Proposals vary; 47-90% reduction, 

2008-2018 implementation. 

National Voluntary Sector 

Initiatives 

Medical, electrical, automotive, 

chlor-alkali 

75% reduction by chlor-alkali sector, 

others pledged. 

State Efforts ECOS, individual states, 

northeastern states 

Reduction goals, programs and 

initiatives 

Product Bans (Use, 

sales, ingredients, etc.) 

Latex paint, seed coatings, 

batteries, fungicides, misc. 

Product bans account for substantial 

emissions reductions to date. 

International Initiatives

International Agreements Aarhus (long-range transport), Basel 

(haz. waste), Stockholm (POPs) 

All address mercury 

United Nations 

Environment Programme 

Established “Capacity Building” 

Mercury Program for developing 

countries 

Concluded in 2003 that mercury is a 

pollutant of concern. 

Commission for 

Environmental 

Cooperation 

U.S., Mexico and Canada Reduce emissions by 50% by 2006 

European Union European Community Legislation on 

Mercury 

All member countries of the EU must 

implement a variety of legislated 

requirements. 

Individual Countries Sweden, others Individual countries, most notably 

Sweden have implemented proactive 

mercury initiatives. 

13 Public Participation 

The goals of public participation include building trust, developing partnerships, encouraging creativity, 

facilitating learning, increasing levels of commitment, maximizing participation, and reaching consensus 

(Smolko et al., 2002). The Agency is committed to a robust effort that meets with a wide range of 

stakeholders, listens to new ideas and approaches, and remains flexible. 

The Agency met with key stakeholders throughout the development of the regional mercury TMDLs, 

including USEPA Region 5 and headquarters. The draft TMDL was available through the Agency 

TMDL web site, a series of public meetings were held across the state, and a 90-day formal public 

comment period ended on October 18, 2005. All comments received during that formal comment period, 

plus Agency responses, will be included in the draft TMDL package that is delivered to Region 5 EPA for 

their review and approval. 

The Agency received more than 975 comments. The summary of the comments, and the Agency 

responses, can be found at http://www.pca.state.mn.us/water/tmdl/tmdl-mercuryplan.html#comments . 

MN Statewide Mercury TMDL 27MAR07_final.doc 51
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MN Statewide Mercury TMDL 27MAR07_final.doc 56
MN Statewide Mercury TMDL 27MAR07_final.doc 
Appendix A 

Impaired Waters Covered by the Statewide 

Mercury TMDL 

MN Statewide Mercury TMDL 27MAR07_final.doc 
MN Statewide Mercury TMDL 27MAR07_final.doc 
MN Statewide Mercury TMDL 27MAR07_final.doc 

Appendix B 

NPDES Permits Covered by the Statewide 

Mercury TMDL