OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

 February 25, 2016

PC Code: 076702

DP Barcode: 429260

MEMORANDUM

SUBJECT: Combined Problem Formulation and Preliminary Risk Assessment in 

Support of the Registration Review of Lime Sulfur

TO: Katherine St. Clair, Chemical Review Manager

Kevin Costello, Branch Chief

Risk Management and Implementation Branch II

Pesticide Re-Evaluation Division (7508P)

FROM: Karen Milians, Ph.D., Chemist

Andrew Sayer, Ph.D., Biologist

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

REVIEWED BY: Thomas Steeger, Ph.D., Senior Science Advisor

BY Jim Carleton, Ph.D., Environmental Scientist

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

THROUGH: Jean Holmes, DVM, MPH, Branch Chief

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

This memorandum transmits the combined problem formulation and preliminary ecological risk 

assessment in support of the Registration Review of calcium polysulfides (PC Code 076702)

hereafter referred to as lime sulfur. The problem formation and preliminary risk assessment (PRA)

were combined because the current database is considered to be sufficient to support the 

Registration Review of lime sulfur given the relatively limited use of the compound as a pesticide. 

The PRA identifies potential risks to non-target organisms; however, for many of these taxa, the 

risk is considered low given the low likelihood of exposure. 

The environmental fate and ecological effects of lime sulfur when used as a fungicide/acaricide

were previously evaluated in 2005 to support the Reregistration Eligibility Decision (RED; DP 
-Page 2 of 30-

Barcode D313165) of inorganic polysulfides1. Since the 2005 RED, no additional data have been 

provided to EPA and risk estimates have not changed from those identified in the RED. While 

acute risk quotients (RQs) exceed levels of concern (LOCs) for aquatic and terrestrial animals, the 

likelihood of actual exposure to residues at levels capable of causing adverse effects in these 

animals is considered low. There is uncertainty however regarding the potential for adverse effects 

to terrestrial invertebrates exposed to lime sulfur from applications made at bloom to pollinatorattractive trees, i.e., apples. Although available contact toxicity data do not suggest that lime sulfur 

is acutely toxic to adult honey bees (Apis mellifera) which serve, for assessment purposes, as a 

surrogate for beneficial terrestrial invertebrates, there are limited anecdotal reports of adverse 

effects to adult bees foraging in orchards during application of lime sulfur to orchards. This 

represents an uncertainty compared to laboratory-based acute studies, but it could be mitigated by 

applying when bees are not active. Additionally, exposure to lime sulfur could be minimalized if 

the compound is applied at times when bee foraging activity is reduced, i.e., early morning or late 

evening. There is also some uncertainty regarding potential risk to terrestrial plants given reported 

incidents involving plants and its use as an apple blossom thinner. Although lime sulfur can move 

from application sites to adjacent surface waters (both freshwater and estuarine/marine) via drift 

from treated areas, the material is expected to rapidly dissociate into products that consist mainly 

of sulfur and calcium ions, which are not believed likely to substantially alter natural background 

levels of these elements in the environment. Consistent with the previous assessments and 

considering the rapid dissociation of lime sulfur, EFED concludes that there is a low likelihood of 

adverse effects to the environment from exposures resulting from the registered use of the 

compound as a fungicide/acaricide. Although there are data to indicate that lime sulfur is not 

acutely toxic to adult honey bees on a contact exposure basis, there is uncertainty regarding the 

potential for adverse effects to non-Apis terrestrial invertebrates and terrestrial plants following 

direct exposure. 

 1 USEPA. 2005. Reregistration Eligibility Decision for Inorganic Polysulfides List D. Case No. 4054. Office of Chemical Safety and Pollution 

Prevention formerly the Office of Prevention, Pesticides and Toxic Substances (7508C). Sept. 30, 2005. 

http://www.epa.gov/pesticides/reregistration/REDs/inorganic_polysulfides_red.pdf
-Page 3 of 30-

Ecological Risk Assessment for the Registration 

Review of Lime Sulfur

CaSx

(x = 2, 3, 4, 5, 6, and 7; predominantly 5)

Calcium Polysulfide (Lime Sulfur)

CAS Registry No: 1344-81-6 PC Code: 076702

Prepared by:

Karen Milians, Ph.D., Chemist

Andrew Sayer, Ph.D., Biologist 

U.S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch IV

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Jean Holmes, DVM, MPH, Branch Chief 

Thomas Steeger, Ph.D., Senior Science Advisor

Jim Carleton, Ph.D., Senior Scientist

February 25, 2016
Page 4 of 30

Table of Contents

1. Executive Summary............................................................................................................ 5

2. Problem Formulation .......................................................................................................... 6

2.1. Mode of Action....................................................................................................... 6

2.2. Use and Usage Characterization ............................................................................. 6

2.4. Previous Risk Assessments..................................................................................... 6

2.5. Water Quality.......................................................................................................... 7

2.6. Stressors of Concern ............................................................................................... 7

2.7. Conceptual Model................................................................................................... 8

2.7.1. Risk Hypothesis...................................................................................................... 8

2.8. Analysis plan........................................................................................................... 8

2.8.1. Ecosystems of Concern........................................................................................... 8

2.8.2. Assessment and Measurement Endpoints............................................................... 9

3. Exposure Characterization.................................................................................................. 9

3.1. Environmental Fate and Transport Summary......................................................... 9

4. Ecological Effects Characterization.................................................................................. 11

4.1. Aquatic Organisms................................................................................................ 11

4.1.1. Freshwater Fish..................................................................................................... 12

4.1.2. Freshwater Invertebrates....................................................................................... 12

4.1.3. Estuarine/Marine Fish........................................................................................... 12

4.1.4. Estuarine/Marine Invertebrates............................................................................. 12

4.1.5. Aquatic Plants and Algae...................................................................................... 13

4.2. Terrestrial Organisms............................................................................................ 13

4.2.1. Avian Taxa............................................................................................................ 14

4.2.2. Terrestrial Invertebrates........................................................................................ 14

4.2.3. Mammals............................................................................................................... 14

4.2.4. Terrestrial Plants................................................................................................... 15

5. Reported Ecological Incidents.......................................................................................... 16

6. Risk Characterization........................................................................................................ 16

7. Endocrine Disruptor Screening Program.......................................................................... 22

8. Endangered Species Assessments..................................................................................... 22

9. Risk Conclusions .............................................................................................................. 24

10. Literature Cited ................................................................................................................. 25

11. Appendix A: The Sulfur Cycle ......................................................................................... 27

12. Appendix B: Output from OPP Aggregate Incident Database for Lime Sulfur ............... 30
Page 5 of 30

1. Executive Summary

Calcium polysulfides, CaSx (also called lime sulfur solution) have fungicidal and secondary 

acaricidal activity and are used to control powdery mildews, anthracnose, scab, spider mites and 

other diseases on alfalfa, clover and fruits. The compound is also used to thin fruit in apple 

orchards. Lime sulfur is an alkaline and corrosive solution containing 29-30% CaSx (where x = 

2, 3, 4, 5, 6, and 7) as the active ingredient (a.i), with the predominant form being the pentasulfide

(pH 11.5-11.8). In addition, minor amounts of calcium thiosulfate (CaS2O3), calcium sulfite 

(CaSO3), sulfur (S), and gypsum (CaSO4·2H2O) may be present. The calcium polysulfides 

rapidly dissociate in the presence of moisture to form calcium cations and anionic and elemental 

sulfur. Given the anticipated rapid dissociation of calcium polysulfides into constituent ions on 

introduction to water, calcium polysulfides are not expected to accumulate in surface water, or to 

accumulate on forage sources in the terrestrial environment. Therefore, there is a low likelihood 

of chronic exposure for aquatic and terrestrial organisms. 

While toxicity tests indicate that the compound ranges from highly to moderately toxic to aquatic 

animals, adverse effects may in large part be based on direct mixing of the active ingredient in 

water with poor buffering capacity in laboratory-based studies and may not be reflective of actual 

exposure conditions under which the compound is expect to rapidly dissociate. For terrestrial 

organisms, lime sulfur is slightly to practically non-toxic to birds (reptiles and terrestrial-phase 

amphibians), moderately toxic to mammals, and practically non-toxic to terrestrial invertebrates

on an acute basis. 

Although risk estimates exceed the level of concern (LOC) for federally listed threatened and 

endangered (listed) and non-listed species of aquatic and terrestrial animals on an acute exposure 

basis, the likelihood of adverse effects from exposure to lime sulfur is considered low given rapid 

dissociation of calcium polysulfide to constituents with very low toxicity under typical 

environmental conditions. Similarly, the likelihood of chronic exposure to the compound and 

hence risk is considered low. Although lime sulfur is practically non-toxic to honey bees (Apis 

mellifera) on an acute contact exposure basis, there is some anecdotal information that bees may 

be adversely affected if applications are made while bees are actively foraging; the likelihood of 

an adverse effects could be reduced though by applying at times when honey bee foraging activity 

is low. Larvae of other beneficial insects may be affected at maximum application rates; however, 

the instability of the compound under most environmental conditions may limit the extent to which 

this occurs. 

Terrestrial plant data are not available, but adverse effects on terrestrial plants have been reported 

following applications of lime sulfur. Also its use as an apple blossom thinner indicate adverse

effects on terrestrial plants. To the extent that lime sulfur adversely affects plants, there can be 

adverse secondary effects to organisms that depend on those plants for forage and habitat. Given 

the uncertainty regarding potential risk to terrestrial plants. Terrestrial plant toxicity data would 

reduce this uncertainty. 
Page 6 of 30

2. Problem Formulation

2.1. Mode of Action

Calcium polysulfides (CaSx or lime sulfur) are inorganic pesticides applied to some agricultural 

crops as a fungicide and/or acaracide. Lime sulfur has been used for over 100 years as a contact 

fungicide/acaricide to control powdery mildews, anthracnose, scab, spider mites and other diseases 

on alfalfa, beans, clover and fruits (Tomlin 1994). The mode of action of calcium polysulfides is 

unknown; however, given the rapid dissociation of calcium polysulfidesin water, chronic exposure 

of aquatic and terrestrial ecosystems to parent calcium polysulfides is not expected. 

2.2. Use and Usage Characterization

Labelled Use

Based on current labels, lime sulfur is registered for feed and food uses on the following crops: 

alfalfa, almonds, apples, blackberries, blueberries, boysenberries, caneberries, cherries (sweet), 

cherries (tart), citrus, clover, currants, deciduous fruit trees, gooseberries, grapes, hazelnuts,

nectarines, oranges, peaches, pears, pecans, pistachio nuts, plums, prunes, quinces, raspberries, 

rye, stone fruits, tangerines, and walnuts. Groupings of major crop uses were based on the 

maximum application rates. Other factors were also considered including application method, 

total acreage of bearing crops that may be treated, and total pounds of lime sulfur applied per year. 

A complete list of these uses and application parameters are included in the 2005 RED and 2015 

new use documents.

Usage

Based on available pesticide usage information for the years 2004 through 2013, the Screening 

Level Uses Analysis of Calcium Polysulfide (SLUA; EPA 2015) provides average annual 

estimates of lime sulfur usage for several crops. The SLUA indicates the greatest usage occurred 

on apples, grapes and pears with on average 900,000 pounds,500,000 and 300,000 pounds of active 

ingredient (lbs. a.i.), respectively, applied annually. 

2.4. Previous Risk Assessments

The most recent assessment of lime sulfur was conducted in 2015 (D422723; USEPA 2015), and 

a previous risk assessment of calcium polysulfides was conducted in 2005. Both assessments have

similar conclusions (D313165, USEPA 2005); given the rapid dissociation of calcium polysulfides

in water, chronic exposure of aquatic and terrestrial ecosystems to parent calcium polysulfides is 

not expected. Therefore, the chronic toxicity guideline studies have previously been waived. Risk 

conclusions from the 2005 RED and the 2015 new use assessment are as follows: 

• listed freshwater fish (as well as aquatic-phase amphibians) are at acute risk from drift;

• acute risk exists to listed and non-listed birds (as well as terrestrial-phase amphibians and 

reptiles);

• acute risk exists to listed and non-listed mammals; and,

• in the absence of terrestrial plant toxicity data, risk may occur to listed and non-listed 

sulfur-sensitive terrestrial plants
Page 7 of 30

The 2005 RED assessment of calcium polysulfides also noted that lime sulfur readily transforms

to calcium hydroxide, Ca(OH)2 and elemental sulfur and that calcium hydroxide is a food additive 

and is generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA). 

According to the sulfur RED, "The human risks, if any, from both dietary and occupational 

exposures are considered to be very low because of the general knowledge of the chemical sulfur, 

its ubiquitous occurrence, and its low toxicity, as well as its long history of use by humans, 

including some pharmaceutical applications." However, sulfur can cause eye and skin irritation 

and EPA has identified the potential hazard for workers re-entering fields following foliar 

application of lime sulfur dust (i.e., eye and skin irritation to people who handle the dust or who 

come into contact with treated foliage during field work). 

Although the previous ecological assessment identified acute risks for freshwater fish resulting 

from spray drift and acute risks for birds and mammals due to direct application based on 

laboratory studies, because of the rapid dissociation of calcium polysulfide to constituents with 

very low toxicity under environmentally realistic conditions, no measures to mitigate potential 

risks to freshwater fish, mammals, or avian species are warranted at this time. 

2.5. Water Quality

Lime sulfur is not identified as a cause of impairment for any water bodies under section 303(d) 

of the Clean Water Act2 (accessed September 10, 2014). In addition, no Total Maximum Daily 

Loads (TMDLs) have been developed for lime sulfur and there are no aquatic life criteria for lime 

sulfur3

. 

2.6. Stressors of Concern

Calcium polysulfides are produced by reacting calcium oxide (CaO; quicklime) or calcium 

hydroxide (Ca(OH)2; slaked lime) with sulfur to produce a highly alkaline solution (pH 11.5-11.8) 

and corrosive product, i.e., CaSx

4

. When released into the moisture-rich compartments of the 

environment, lime sulfur is expected to transform (dissociate) quickly into polysulfide anions 

(which in turn is quickly converted to sulfur in various forms “S”) and calcium cations (Ca2+). 

Elemental anionic sulfur and calcium cations are ubiquitous in the environment and the amounts 

of calcium and sulfur incorporated into the ecosystem from the use of calcium polysulfides are 

considered negligible. Therefore, only the parent compound (undissociated form of CaSx

5

) is the 

stressor of concern.

 2 http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885

3 http://www.epa.gov/waterscience/criteria/aqlife/index.html

4

The registrant submitted information on the product chemistry of the pesticide (MRID 43894401) and on its 

chemical identity (MRID 41769502). Both submissions are not guideline studies.

5

The registrant submitted information on the product chemistry of the pesticide (MRID 43894401) and on its 

chemical identity (MRID 41769502). Both submissions are not guideline studies.
Page 8 of 30

2.7. Conceptual Model

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure.

The conceptual model for lime sulfur provides a written description of the predicted relationships 

between the potential routes of exposure to lime sulfur and the predicted effects for the assessment 

endpoint (USEPA 1998).

As discussed previously, several ecological risk assessments have been conducted by EFED for 

lime sulfur, including a national level risk assessment supporting the reregistration eligibility 

decision (USEPA 2005).

2.7.1. Risk Hypothesis

A risk hypothesis describes the predicted relationship among the stressor, exposure, and assessment 

endpoint response along with the rationale for their selection. For lime sulfur, the following ecological risk 

hypothesis is being employed for this PRA:

Based on the most sensitive toxicity values, direct exposure to calcium polysulfides from their use 

as a fungicide/acracide may result in acute and chronic adverse effects to non-target aquatic 

(freshwater fish) and terrestrial (birds and mammals) organisms as a result of the registered use 

of the compound. Acute adverse effects to non-target terrestrial plants and beneficial insects are 

also possible. 

2.8. Analysis plan

2.8.1. Ecosystems of Concern

Aquatic Environment

The environmental fate properties and use patterns of lime sulfur indicate that the compound 

dissociates rapidly and is not likely to move directly into surface water except as spray drift; 

however, exposure of aquatic ecosystems through spray drift is likely to be reduced through the 

large volume and natural buffering capacity of most receiving waters as well as oil formulations 

of lime sulfur which limit the extent to which drift may occur. However, while direct exposure to 

lime sulfur can result in acute adverse effects on aquatic ecosystems in poorly buffered systems, 

the rapid dissociation of the compound in water is expected to reduce the likelihood of such effects. 

The likelihood of chronic adverse effects on aquatic ecosystems is considered low given the rapid 

dissociation of the compound. 

Terrestrial Environment
Page 9 of 30

Exposure of terrestrial vertebrates (e.g., birds, mammals, reptiles, terrestrial-phase amphibians)

and invertebrates (e.g., insects), and terrestrial plants to lime sulfur from direct spray drift from 

labeled use of the pesticide may cause reduced survival, growth, and reproduction to terrestrial 

invertebrates. Terrestrial organisms may be subject to acute exposure to the parent compound

from direct contact on-site or through drift to adjacent areas, however, similar to aquatic 

environments, lime sulfur is expected to rapidly dissociate in terrestrial environments to its nontoxic constituent (elemental forms of calcium and sulfur) that do not substantially alter natural 

background levels of these compounds. In a worst case scenario, the application of lime sulfur on 

the terrestrial environment at the highest application rate will lower (acidify) acidic or neutral soils 

by less than 0.5 pH units. This is further discussed in Section 6.

2.8.2. Assessment and Measurement Endpoints

Assessment endpoints represent the actual environmental value that is to be protected, defined by 

an ecological entity (species, community, or other entity) and its attribute or characteristics 

(USEPA 1998). For lime sulfur, the ecological entities include the following: birds, amphibians, 

reptiles, mammals, freshwater fish and invertebrates, estuarine/marine fish and invertebrates, 

terrestrial plants, insects, and aquatic plants and algae. The attributes assessed for each of these 

entities may include growth, survival, and reproduction. The assessment endpoints are intended 

to reflect population sustainability and community structure within ecosystems and hence relate 

back to ecosystems at risk. If risks are expected for given species/taxa based on the screeninglevel assessment, then risks might be expected to translate to higher levels of biological 

organization.

Measurement endpoints are standardized so that acute toxicity is represented by levels that result 

in mortality to 50% of tested individuals (i.e., LC50, LD50 and EC50) and chronic toxicity is 

represented as a no observed adverse effect concentration or level (i.e., NOAEC or NOAEL). 

Tables 1 and 2 include the most sensitive toxicity endpoints available for lime sulfur that will be 

used to assess risks to terrestrial and aquatic organisms. 

3. Exposure Characterization

3.1. Environmental Fate and Transport Summary

The environmental fate of lime sulfur was previously evaluated (in 2005) to support the RED for 

inorganic polysulfides6 and was more recently assessed to support a new use of lime sulfur to thin 

fruit in apple orchards (USEPA, 2015). Since publication of the 2005 RED, no additional 

environmental fate data have been provided to EPA. 

 6 USEPA. 2005. Reregistration Eligibility Decision for Inorganic Polysulfides List D. Case No. 4054. Office of Chemical Safety and Pollution 

Prevention formerly the Office of Prevention, Pesticides and Toxic Substances (7508C). Sept. 30, 2005. 

http://www.epa.gov/pesticides/reregistration/REDs/inorganic_polysulfides_red.pdf
Page 10 of 30

As noted in the 2005 RED, calcium polysulfides dissociate in water into calcium cations and 

polysulfide anions (which in turn transform into sulfur in various forms), and therefore the fate of 

this pesticide in the aqueous environment is dependent on the fate of its dissociation products. In 

this respect, two important factors are considered: the first is the expected change in environmental 

background levels of calcium ions and sulfur due to application of the pesticide; and, the second 

is the fate and transport of these dissociation products.

With respect to changes in the environment due to applications of lime sulfur, the use patterns

and/or application rates of lime sulfur are not expected to increase the total calcium or sulfur 

content of soils above typical background levels. 

In considering the second factor, the RED noted that both calcium ions and sulfur react with other 

substances found in the environment, forming various calcium- and sulfur-containing compounds. 

Sulfur in its elemental form is relatively immobile, as it is highly insoluble and largely precipitates 

out of solution. Other forms such as thiosulfate may remain in solution and form complexes with 

metals commonly found in the natural environment. The fate of sulfur is dependent upon the 

characteristics of the environment in which it is found (i.e., soil, water/sediment or surface water), 

and is largely determined by the oxidation/reduction potential of the system and the type of 

microorganisms present (refer to the sulfur cycle in Appendix A). Under oxidizing conditions

(e.g., in aerobic soils or surface water) elemental sulfur is oxidized to sulfate by autotrophic 

bacteria. Under sufficiently low oxidizing conditions (e.g., in anaerobic soil/sediments) sulfate is 

reduced to sulfide, which may be found in forms including hydrogen sulfide (H2S), bisulfide (HS1

), and free sulfide anion (S-2). 

Hydrogen sulfide is a weak acid, while bisulfide and free sulfide are strong bases; the relative 

proportions of these three chemical entities will thus largely be governed by the pH of the medium. 

Sulfide may react with iron and other transition metals to form insoluble precipitates. Hydrogen 

sulfide itself is somewhat volatile and may evaporate to some extent. The 2005 RED concluded 

that it is unlikely that elevated levels of hydrogen sulfide will form in the environment as a result 

of the agricultural use of calcium polysulfides because the amount of sulfur added into the sulfur 

cycle from usage of these products is unlikely to substantially contribute to the pool of sulfur 

already present in reducing environments. 

Calcium polysulfides are produced by reacting lime with sulfur in boiling water resulting in a 

concentrated alkaline solution (pH 11.5-11.8). Application of calcium sulfides to targeted 

foliage/soils and its movement to water bodies by drift results in low concentrations of calcium 

polysulfides in these systems. Such quantities are not believed likely to significantly alter natural 

background levels of these elements in the environment nor are they expected to substantially alter 

the pH of receiving waters because of natural buffering capacity typically present. Such additions 

might potentially cause small increases in the pH of a water body that has low buffering capacity; 

however, minor fluctuations in pH are not expected to have direct impact on the aquatic life 

contained therein. Refer to Appendix A where an analysis of the contribution from spray drift 

alone in a low buffering capacity environment was simulated in soil and aqueous environment. 

The results of that analysis indicate that when using the maximum annual application rate of lime 

sulfur, spray drift will not significantly change the pH of the aquatic environment and therefore, is 
11

not expected to adversely impact aquatic life. Similarly, when lime sulfur is applied at the 

maximum application rate to soils with low buffering capacity, the pH in soil will not be impacted 

significantly.

The fate of lime sulfur depends on the fate of its dissociation products: calcium and sulfur. Calcium 

cations can be found naturally in the environment and are not expected to cause an adverse effect 

by their release. After application, polysulfides enter the sulfur cycle. The main processes and 

dissipation of elemental sulfur are oxidation to sulfate (SO4

2-

; produced in soils under aerobic 

conditions when bacteria are growing) and reduction to sulfide (S2-; under anaerobic conditions). 

Both of these processes are mainly mediated by microbes. The dissipation of SO4

2- is dependent 

on leaching and soil organic matter immobilization (USEPA, 2013). The fate of S2- is dependent 

on metal sulfide precipitation or volatilization of H2S. The oxidation of sulfur leads to formation 

of sulfuric acid. The sulfuric acid will dissociate to form hydrogen ions and sulfate ion (SO4

-2

),

which may decrease the pH of some soils and shallow water bodies.

The oxidation reaction that occurs is as follows, wherein hydrogen ions (H+) are liberated into the 

soil environment, potentially decreasing soil pH:

CO2 + S0+ 1⁄2O2 + 2H2O → CH2O + SO4

2-

+ 2H+

Sulfate ions may interact with calcium (Ca2+) and magnesium ions (Mg2+) in water to form sulfate 

(SO4) salts. Hydrogen ions will generally be neutralized by the carbonate buffering system.

Calcium ions react with carbonate ions to form calcium carbonate. The dissolved carbonate ion 

acts as a base and produces bicarbonate ion and hydroxide ion in the water (Baird, 2003). 

Ca2+ + CO3

-2  CaCO3

CaCO3 + H2O  Ca2+ + HCO3

- + OHElemental sulfur, in fact, is used as an amendment to supplement soil fertility and it is utilized on 

crops as a fungicide/acaracide (EPA Reg. No. 2935-407, PC code 077501). 

Considering the previously-recognized rapid dissociation of calcium polysulfide, and that no 

additional data have been identified to alter and/or contradict the previous assessments, EPA’s 

understanding of the environmental fate of lime sulfur has not changed.

4. Ecological Effects Characterization

A detailed description of the available ecotoxicity data for lime sulfur is provided in the 

Environmental Fate and Ecological Risk Assessment written in support of the RED for calcium 

polysulfides (USEPA 2005). Since the completion of that assessment, no new ecological effects

data on lime sulfur have been submitted to the EPA. 

4.1. Aquatic Organisms
12

Lime sulfur is categorized as highly toxic to freshwater fish and is moderately toxic to freshwater 

invertebrates on an acute exposure basis. Since freshwater fish serve as surrogates for aquaticphase amphibians, lime sulfur is categorized as highly toxic to this taxon as well. No data are 

available to assess the toxicity of lime sulfur to estuarine/marine animals. Exposure to lime sulfur 

altered the pH and dissolved oxygen content of the test water and resulted in decreased number of 

eggs hatched in benthic aquatic invertebrates. In a worst case scenario, the application of lime 

sulfur on the terrestrial environment at the highest application rate will lower (acidify) poorlybuffered aquatic habitats (such as a pond) by less than 0.5 pH units. This is further discussed in 

Section 6. Given the rapid dissociation of lime sulfur, chronic toxicity studies have been waived. 

An overview of submitted aquatic organism studies can be seen in Table 1.

4.1.1. Freshwater Fish

The acute toxicity of lime sulfur (calcium polysulfides) formulation (29% active ingredient) was 

evaluated in the freshwater rainbow trout (Oncorhynchus mykiss; McCann 1976), fathead minnow 

(Pimphales promelas; MRID 40098001), and bluegill sunfish (Lepomis macrochirus; MRID 

40098001). The most sensitive freshwater fish tested was the rainbow trout with a 96-hour LC50

value of 0.97 mg a.i./L. Based on this information, lime sulfur is categorized as highly toxic to 

freshwater fish on an acute exposure basis. Toxicity data are not available for aquatic vascular 

plants; however, exposure of the nonvascular green algae to lime sulfur resulted in a 120-hr EC50

of 14.1 mg/L. 

4.1.2. Freshwater Invertebrates

The acute toxicity of lime sulfur formulation (29% a.i.) was evaluated in two species of

invertebrates, i.e., water fleas, Daphnia pulex (MRID 40098001) and Simocephalus serrulatus 

(MRID 40098001), with reported 48-hour LC50 values of 2.9 mg a.i./L and 3.2 mg a.i./L, 

respectively. Based on these results, lime sulfur (calcium polysulfides) is categorized as 

moderately toxic to freshwater invertebrates on an acute exposure basis. 

 

The effects of acute exposure (72 hours) of lime sulfur (calcium polysulfides) was examined on 

egg hatchability in the midge (Chironomus riparius), a freshwater benthic invertebrate. Results 

of this study demonstrate a dose-dependent decrease in egg hatchability, with an estimated 

NOAEC of 3.2 mg/L (Wegner and Hamilton 1976). Due to several confounding factors, including 

concentration-dependent increase in pH and decrease in dissolved oxygen, results are not suitable 

for quantitative use in risk assessment. 

4.1.3. Estuarine/Marine Fish

No data are available to assess the acute toxicity of lime sulfur to estuarine/marine fish.

4.1.4. Estuarine/Marine Invertebrates

No data are available to assess the acute toxicity of lime sulfur to estuarine/marine invertebrates.

Chronic Effects
13

EFED waived the data requirements for chronic toxicity studies of aquatic organisms due to the 

rapid dissociation of lime sulfur in the environment and low likelihood of chronic exposure.

4.1.5. Aquatic Plants and Algae

The toxicity of lime sulfur was evaluated in the nonvascular aquatic green algae 

(Pseudokirchneriella subcapitata formerly Selenastrum capricornutum; MRID 43960801). 

Results of this study showed 120-hour EC05 and EC50 values of 0.5 mg a.i./L and 14.1 mg a.i./L, 

respectively. 

No further information is available regarding the potential effects of lime sulfur exposure to aquatic 

vascular or nonvascular plants.

Table 1: Lime Sulfur Acute Toxicity Values for Aquatic Animals.

4.2. Terrestrial Organisms

Lime sulfur is categorized as slightly toxic to birds on an acute oral exposure basis and as 

practically nontoxic to birds on a subacute dietary exposure basis; the compound is categorized as 

moderately toxic to mammals on an acute oral exposure basis. Since birds serve as surrogates for 

reptiles and terrestrial-phase amphibians, the same toxicity classification applies to these taxa. 

While lime sulfur is practically non-toxic to honey bees on an acute contact exposure basis, 

Species

Lime Sulfur

(Calcium Polysulfides)

Toxicity Value in mg/L

(MRID)

Test Material

Rainbow trout

(Oncorhynchus mykiss)

96-hour LC50=0.97 

(McCann 1976)a

29% formulation

(Miller Lime Sulfur Solution)

96-hour LC50=2.4

(40098001)a

29% formulation

Bluegill sunfish

(Lepomis macrochirus)

96-hour LC50=14.1

(40098001)

a

29% formulation

Fathead minnow

(Pimephales promelas)

96-hour LC50=9.2 

(40098001)

a

29% formulation

Waterflea

(Daphnia pulex) 48-hour LC50=2.9 (40098001)

a 29% formulation

Waterflea

(Simocephalus serrulatus) 48-hour LC50=3.2 (40098001)

a 29% formulation

a Study report did not specify if toxicity endpoints were expressed in terms of mg formulation/L or mg a.i./L. 
14

exposure to other insects resulted in mortality at application rates below current maxima. Given 

the rapid dissociation of lime sulfur, chronic toxicity studies have been waived. No data are 

available to assess the toxicity of lime sulfur to terrestrial plants. An overview of submitted 

terrestrial organism studies can be seen in Table 2.

4.2.1. Avian Taxa 

The acute oral exposure of bobwhite quail (Colinus virginianus) to lime sulfur resulted in an LD50

value of 560 mg a.i./kg bw (MRID 43945101). Based on this study, lime sulfur is classified as 

slightly toxic to birds (and to reptiles and terrestrial-phase amphibians for which birds serve as 

surrogates) on an acute oral exposure basis. Treatment-related clinical signs and gross pathology

in the acute oral toxicity study in bobwhite quail included ataxia, hyporeactivity, immobility, crop 

damage, gastric ulcers and hemorrhaging (location not specified). 

The subacute dietary toxicity of lime sulfur was evaluated in bobwhite quail (MRID 43945103) 

and mallard ducks (Anas platyrhynchus; MRID 43945104). Both studies yielded LC50 values 

>5,000 mg a.i./kg diet. Based on these results, lime sulfur is categorized as practically non-toxic 

to birds on a subacute dietary exposure basis. No clinical signs or gross pathology were observed 

in the subacute dietary studies in bobwhite quail and mallard ducks. 

4.2.2. Terrestrial Invertebrates

The acute contact laboratory-based study of honey bees with lime sulfur resulted in a 48-hr. LD50

>25 μg a.i./bee (MRID 43945102); therefore, lime sulfur is classified as practically non-toxic to 

adult honey bees on an acute contact exposure basis. However, there are limited anecdotal reports 

of adverse effects to adult bees foraging in orchards during application of lime sulfur to orchards; 

however, these reports are not consistent with the laboratory-based acute toxicity data. This 

represents an uncertainty.

In addition to the acute contact study in honey bees, the acute toxicity of formulated calcium 

polysulfides to non-target beneficial insects has been reported in the open literature. These studies 

have included parasitic wasps (e.g., Aphytis lophanthae) (Bartlett 1966; 1973), predatory beetles

(e.g., Cryptolaemus montrouzieri; Bartlett 1966; 1973) and predatory mites (e.g., Typhlodromus 

doreenae) (Bartlett 1964; James and Rayner 1995). Results show that exposure to calcium 

polysulfides at levels consistent with label-recommended rates does result in mortality of these 

non-target beneficial insects under the conditions tested. 

4.2.3. Mammals

In an acute oral toxicity study with Sprague-Dawley rats (Rattus norvegicus) administered single 

doses of a calcium polysulfides formulation, the acute LD50 values for male and female rats 

were119 mg a.i./kg bw and 86.6 mg a.i./kg bw, respectively (Accession No. 00154738). Based on 

these result, lime sulfur is classified as moderately toxic to mammals on an acute oral exposure 

basis. However, treatment-related sublethal effects were reported in this study and included ataxia,

convulsions, lethargy, morbidity, diarrhea, and weight loss. Gross pathology findings included 

enlarged adrenal glands, discolored liver, and dark red lungs, kidneys, and spleen. 
15

Chronic Effects

Data for chronic toxicity studies to terrestrial organisms are not required due to the rapid 

dissociation of lime sulfur in the environment and an incomplete chronic exposure pathway.

4.2.4. Terrestrial Plants

No data have been submitted to the EPA to characterize risks from application of lime sulfur to 

terrestrial plants. Based on the use of lime sulfur to thin apple blossoms along with incident 

reports, lime sulfur can affect abscission in plants and may have the capacity for non-target 

phytotoxicity. 

Table 2: Lime Sulfur Acute Toxicity Values for Terrestrial Animals. 

Exposure 

Scenario Species Test Material Toxicity Reference Value

Reference MRID

(Classification)

Mammals

Acute (Dosebased) Rat

Orthix Spray 

(aqueous 

product 

containing 

16.66% a.i.)

LD50 = 86.63 mg a.i./bw.

a

(single oral dose)

Accession No. 

00154738 

(Acceptable)

Birds

Acute (Dosebased)

Bobwhite 

quail

(Colinus 

virginianus)

29% 

formulation

LD50 = 560 mg a.i./kg bw

(single oral dose)

43945101 

(Acceptable)

Acute (Dietarybased)

Bobwhite 

quail

(Colinus 

virginianus)

and

Mallard duck

(Anas 

platyrhynchus)

29% 

formulation

LC50 >5000 mg a.i./kg diet

(for both species)

(5-day dietary)

43945103 quail 

(Acceptable)

43945104 duck

(Acceptable)

Terrestrial invertebrates

Acute contact

Honey bee

(Apis 

mellifera)

29% 

formulation

LD50 > 25 ug a.i./bee

(single contact dose)

43945102 

(Acceptable)

a The study report did not specify if toxicity endpoints were expressed in terms of mg formulation/L or mg a.i./L. 
16

5. Reported Ecological Incidents

The ecological incident information system (EIIS) is a database maintained by the Office of 

Pesticide Programs; the database contains ecological incidents that have been reported to the EPA. 

When available, EIIS includes date and location of an incident, type and magnitude of effects 

observed in various species, use(s) of pesticides known or suspected of contributing to the incident, 

and results of any chemical residue analysis or other analyses conducted during incident 

investigation. EIIS incidents are categorized according to the certainty that the incident resulted 

from pesticide exposure. The Avian Incident Monitoring System (AIMS) is a database 

administered by the American Bird Conservancy that contains publicly available data on reported 

avian incidents involving pesticides. Many of the incidents listed in this database are also in the 

EIIS. Because of uncertainties regarding the extent to which incidents are reported to EPA, the 

absence of incident reports cannot be construed as the absence of incidents. This database was 

searched in December 2014 and returned no incidents related to the use of lime sulfur.

Based on the 40 CFR §159.184, information on all known “major” incidents must be submitted to 

the EPA by the registrant(s). EIIS contained one incident for lime sulfur. The incident, which 

took place in Illinois and was reported in March 2001, caused plant damage on 160 acres of directly 

treated corn and was listed as “possibly” caused by lime sulfur (based on the certainty index). It 

was undetermined if the incident was due to a misuse of the product.

All ecological incidents considered “minor” only need to be aggregately reported in Aggregate 

Incident Reports (AIR) as quarterly counts of incidents by the registrant(s). The incidents listed 

in this database may also appear in the EIIS. From the AIR, a total of six minor incidences were 

reported between April1995 and June 2012 (Appendix B). All of these incidences involved minor 

plant damage; however it is uncertain whether these incidents occurred as a result of a direct 

application to the affected plants at registered rates. Because of uncertainties regarding the extent 

to which incidents are reported to EPA, the absence of incident reports cannot be construed as the 

absence of incidents. 

6. Risk Characterization

Risk characterization is the integration of exposure and effects characterization to determine the 

ecological risk from the use of calcium polysulfides and the likelihood of effects on aquatic life 

and wildlife based on varying pesticide-use scenarios. The risk characterization articulates risk 

assessment assumptions, limitations, and uncertainties. No new data have been submitted or 

reviewed by the EPA.

As stated in the 2005 RED, calcium polysulfides are assumed to react quickly in the environment; 

runoff and/or leaching of the intact parent compound into nearby water bodies is assumed to be 

negligible. Therefore, estimates of calcium polysulfides for aquatic ecosystems were based on 

drift alone using the model AGDRIFT. AGDRIFT estimates the fraction of pesticide that is 

released indirectly to a water body due to spray drift following a typical aerial or ground based 

application to a crop. Drift alone was considered since the likelihood of runoff of the intact 
17

material from treatment zones is low given the rapid dissociation of the material. Application 

rates ranging from approximately 3 lbs a.i./A (alfalfa) to 67 lbs a.i./A (blueberries and grapes) 

were employed to estimate the fraction of spray drift and loading of calcium polysulfides to a water 

body downwind from the release site. Initial concentrations of parent calcium polysulfides, in 

surface water ranged from less than 0.7 micrograms per liter (μg a.i./L) to approximately 120 μg 

a.i./L, depending upon the application rate and method. Although monitoring data do not exist for 

calcium polysulfides in natural waters, background levels of its dissociation products of sulfur and 

calcium are usually in the milligram per liter (mg/L) range. Estimated concentrations of the 

dissociation products from the maximum estimated concentration of calcium polysulfides (the 12 

μg a.i./L) results in a maximum “Ca+” content of 24 μg a.i./L and a maximum sulfur “S-

” content 

of 96 μg a.i./L 7 being added to water bodies due to spray drift loading and are well below the 

ambient levels of these compounds in natural waters.

In the biosphere, sulfur produced from calcium polysulfides becomes incorporated into the global 

sulfur cycle (see Appendix A) and its fate in the environment is dependent upon the 

oxidation/reduction potential of the soil, sediment or water system, and the type of microorganisms 

present.

The EFED terrestrial exposure model T-REX was used to estimate exposures and risks to avian 

and mammalian species for single spray applications of calcium polysulfides at rates ranging from 

approximately 3 lbs a.i./A (alfalfa) to 67 lbs a.i./A (blueberries and grapes). The model provides 

estimates of exposure concentrations and calculates risk quotients (RQs) for three body weight 

classes each for birds and mammals. In the calculation, the model uses chemical residues on the 

surface of different types of foliage that may be sources of exposure to avian, mammalian, 

reptilian, or terrestrial-phase amphibian receptors. Maximum residues of calcium polysulfides 

ranged from 46 mg a.i./kg diet for fruits/pods/large insects from application to alfalfa to 15,979 

mg a.i./kg diet for short grass from application to blueberries. However, these exposure estimates 

do not consider the extent to which the compound is subject to rapid dissociation.

Toxicity data and exposure estimates for lime sulfur are used to evaluate the potential for adverse 

ecological effects on non-target species. This screening-level assessment employs a deterministic 

risk estimation method, based on RQ values, to provide a metric of potential risks. The potential 

for risk is based on the risk estimation results and other relevant information about toxicity and 

ecosystems potentially at risk, and the environmental fate and transport characteristics of lime 

sulfur. Unitless RQ values are compared to the EPA’s LOCs to identify taxonomic groups 

potentially at risk of acute or chronic effects associated with lime sulfur’s registered uses. 

For a complete overview of the risk estimation and risk characterization, refer to the 2005 RED. 

Tables 3 through 6, taken from the 2005 RED, are presented below. Briefly, acute RQ values 

exceed LOCs for acute risk to aquatic and terrestrial animals. The highest exceedances are 

associated with the highest application rate (i.e., blueberries; 66.58 lbs a.i./A) and lowest for alfalfa 

 7 Calculation is based on an assumption that the compound is 100% CaS5 that is 80% “S” plus 20% o “Ca+ ions” 

(Based on a molecular weight conversion).
18

(3.07 lbs a.i./A) for each of the crop groupings assessed. The 2015 new use assessment (D422723) 

evaluated the proposed use of lime sulfur to thin fruit in apple orchards; the blueberry application 

rate modelled below is similar to the maximum rate used to thin apples (i.e., 66.58 and 71.28 lbs 

a.i./A for blueberries and apples, respectively). 

Table 3. Acute RQs for Freshwater Fish and Freshwater Invertebrates Exposed to Calcium Polysulfides Based 

on Maximum Application Rates

Crop Use (Application Rate)

Application 

Type

EEC

(mg a.i./L)

Acute RQa

Freshwater Fish Freshwater 

Invertebrate

Blueberries (66.58 lb a.i./A) Aerial 0.11971 0.12b 0.041

Grapes (61.48 lb a.i./A)

Aerial 0.11054 0.11b 0.038

Air blast 0.000651 0.0007 0.00022

Almonds (49.18 lb a.i./A) Aerial 0.08843 0.091b 0.030

Apples (33.81 lb a.i./A) Aerial 0.06079 0.063b 0.021

Alfalfa (3.07 lb a.i./A) Aerial 0.00553 0.0057 0.0019

a

RQs = EEC/LC50, where EECs are the peak concentrations in surface water generated from AGDRIFT, and acute toxicity reference values 

are as follows: freshwater fish, rainbow trout 96-hr LC50 = 0.97 mg a.i./L; freshwater invertebrates, waterflea 48-hr EC50 = 2.9 mg a.i./L. b

RQs exceed LOC for acute risk to listed species (LOC 0.05).

 

Although Table 3 indicates that acute risk LOCs are exceeded for listed fish based on estimated 

environmental concentrations in water, lime sulfur is not directly applied to water; therefore, its 

potential movement into surface water would be limited to drift. Current oil formulations would 

reduce the amount of lime sulfur available to reach water bodies via drift and the analysis of drift 

discussed earlier indicates that neither background levels of calcium and sulfur nor pH would 

likely be substantially affected. Lime sulfur applied in the terrestrial environment is expected to 

degrade into its constituent elements, the addition of which to soil is not expected to cause

significant deviations from background or ambient levels of calcium and sulfur. During a runoff 

event (i.e., overland flow of water following a period of precipitation), negligible amounts of lime 

sulfur would be expected to enter a water body, due to the rapid dissociation of the compound in 

soils. Therefore, the likelihood of adverse effects on fish and aquatic-phase amphibians from the 

use of lime sulfur is considered low due to the low likelihood of exposure. Although no data are 

available to assess the potential toxicity of lime sulfur to estuarine/marine organisms, similar to 

freshwater organisms, the likelihood of exposure is considered low. 

Table 4. RQs for Listed and Non-Listed Aquatic Non-vascular Plants Exposed to Calcium Polysulfides

Crop Use (Application Rate) Application 

Type

EEC

(mg a.i./L)

RQa

Non-Listed Aquatic Algae Listed Aquatic Algae

Blueberries (66.58 lb a.i./A) Aerial 0.11971 0.00849 0.2
19

Crop Use (Application Rate) Application 

Type

EEC

(mg a.i./L)

RQa

Non-Listed Aquatic Algae Listed Aquatic Algae

Grapes (61.48 lb a.i./A) Aerial 0.11054 <0.01 0.2

Air blast 0.000651 <0.01 <0.01

Almonds (49.18 lb a.i./A) Aerial 0.08843 <0.01 0.2

Apples (33.81 lb a.i./A) Aerial 0.06079 <0.01 0.1

Alfalfa (3.0 lb a.i./A) Aerial 0.00553 <0.01 0.01

a

RQs = EEC/LC50, where EECs are the peak concentrations in surface water generated from AGDRIFT, and acute toxicity 

reference values are as follows for the nonvascular aquatic plant Pseudokirchneriella subcapitata: non-listed species 120-hour 

EC50 =14.1 mg a.i./L; listed algae 120-hour EC05 =0.5 mg a.i./L

Laboratory-based studies indicate that lime sulfur is slightly toxic to birds on an acute oral 

exposure basis; however, the compound is practically non-toxic to birds (and terrestrial-phase 

amphibians and reptiles) on a subacute dietary exposure basis. While the acute oral toxicity test 

was conducted according to guideline specifications, the likelihood that birds (and terrestrial-phase 

amphibians and reptiles) would voluntarily consume a caustic solution is considered low; 

therefore, the subacute dietary toxicity test is considered to be a more realistic indicator of toxicity 

to lime sulfur residues on dietary forage items. Although Table 5 indicates that dose-based RQs

exceed acute risk LOCs across the uses assessed, subacute dietary toxicity data indicate that the 

LC50 exceeded the highest dietary concentration tested, i.e., LC50>5,000 mg/kg diet. Residues on 

terrestrial forage items are subject to the same processes that occur in soil and lime sulfur is 

expected to rapidly dissociate to constituents that are generally regarded as safe; therefore, the 

likelihood of exposure by birds to elevated levels of the parent compound is considered low. EFED 

cannot estimate the extent to which RQ values reported in Table 5 would be reduced; however, 

based on available data, current uses of lime sulfur do not appear to represent an actual risk to 

birds, terrestrial-phase amphibians or reptiles. Similar to aquatic habitats, the likelihood of chronic 

exposure to lime sulfur is considered low given the rapid dissociation of the compound; therefore, 

the likelihood of adverse chronic effects from the compound is considered low.

Table 5. Dose-based Acute RQs for Birds Exposed to Calcium Polysulfides as Calculated by T-REX Based on 

Maximum Application Rates

Crop Use

(Application 

Rate)

Body

Weight 

(g)

Avian Risk Quotientsa

Short 

Grass

Tall Grass Broadleaf Plants/Small 

Insects

Fruits/Pods/Large 

Insects

Blueberries

(66.58 lb a.i./A)

20 45.95b 21.06b 25.85b 2.87b

100 29.07b 13.32b 16.35b 1.82b

1,000 8.27b 3.79b 4.65b 0.52b

Grapes 20 42.43b 19.45b 23.87b 2.65b
20

Crop Use

(Application 

Rate)

Body

Weight 

(g)

Avian Risk Quotientsa

Short 

Grass

Tall Grass Broadleaf Plants/Small 

Insects

Fruits/Pods/Large 

Insects

(61.48 lb a.i./A) 100 26.84b 12.30b 15.10b 1.86b

1,000 7.64 3.50b 4.30b 0.48c

Almond

(49.18 lb a.i./A)

20 33.94b 15.56b 19.09b 2.12b

100 21.47b 9.84b 12.08b 1.34b

1,000 6.11b 2.80b 3.44b 0.38c

Apples

(33.81 lb a.i./A)

20 23.34b 10.70b 13.13b 1.46b

100 14.76b 6.77b 8.30b 0.92b

1,000 4.20b 1.93b 2.36b 0.26c

Alfalfa

(3.07 lb a.i./A)

20 2.12b 0.97b 1.19b 0.13c

100 1.34b 0.61b 0.75b 0.08

1,000 0.38c 0.17c 0.21c 0.02

a Acute dose-based RQ = EEC/LD50, where EEC values are upper bound residues expressed as equivalent dose (mg a.i./kg body weight) 

generated from T-REX and the toxicity value is the acute dose-based LD50 =560 mg a.i./kg diet in bobwhite quail. bRQs are above the LOC for acute risk to both non-listed (LOC 0.5) and listed species (LOC 0.1). c RQs are above the LOC for acute risk to listed species (LOC 0.1).

Similar to the situation for birds and based on the dose-based RQ values reported in Table 6, acute 

risk LOCs are exceeded for mammals. However, the likelihood of mammals willingly consuming 

a caustic solution of lime sulfur seems remote. While subacute dietary toxicity data are not 

available for mammals, the RQ values reported in Table 6 are not considered an accurate 

representation of the potential risk. Again though, EFED cannot estimate the extent to which RQ 

values would be reduced; however, based on available data, current uses of lime sulfur do not 

appear to represent an actual risk to mammals. As noted previously, likelihood of chronic exposure 

to lime sulfur is considered low given the rapid dissociation of the compound; therefore, the 

likelihood of adverse chronic effects from the compound is considered low.

Table 6. Dose-Based Acute RQs for Mammals Exposed to Calcium Polysulfides Calculated by T-REXa Based 

on Maximum Application Rates

Crop Use

(Application 

Rate)

Body 

Weight

(g)

Mammalian Acute Risk Quotientsb 

Short 

Grass

Tall Grass Broadleaf 

Plants/Small 

Insects

Fruits/Pods/Large 

Insects

Seeds

 

Blueberries

(66.58 lb a.i./A)

15 79.73c 36.54c 44.85c 4.98c 1.10c

35 68.46c 31.38c 38.51c 4.28c 0.97c
21

Crop Use

(Application 

Rate)

Body 

Weight

(g)

Mammalian Acute Risk Quotientsb 

Short 

Grass

Tall Grass Broadleaf 

Plants/Small 

Insects

Fruits/Pods/Large 

Insects

Seeds

1,000 35.97c 16.49c 20.23c 2.25c 0.45d

Grapes

(61.48 lb a.i./A)

15 73.62c 33.74c 41.41c 4.60c 1.02c

35 63.22c 28.97c 35.56c 3.95c 0.90c

1,000 33.22c 15.22c 18.68c 2.08c 0.42d

Almond

(49.18 lb a.i./A)

15 58.89c 26.99c 33.13c 3.68c 0.81c

35 50.57c 23.18c 28.44c 3.16c 0.72c

1,000 26.57c 12.18c 14.95c 1.66c 0.33d

Apples

(33.81 lb a.i./A)

15 40.49c 18.56c 22.78c 2.53c 0.56c

35 c 34.77c 15.94c 19.56c 2.17c 0.49d

1,000 18.27c 8.37c 10.28c 1.14c 0.23d

Alfalfa

(3.07 lb a.i./A)

15 3.68c 1.68c 2.07c 0.23d 0.05

35 3.16c 1.45c 1.78c 0.20d 0.04

1,000 1.66c 0.76c 0.93c 0.10d 0.02

a EECs values are upper-bound residues expressed as equivalent dose (mg a.i./kg body weight) generated from T-REX. b RQs calculated using the acute oral LD50 value = 86.63 mg a.i./kg body weight in male rats. c RQs are above the LOC for acute risk to both non-listed (LOC 0.5) and listed species (LOC 0.1). d RQs are above the LOC for acute risk to listed species (LOC 0.1)

 

While no terrestrial plant toxicity studies were submitted, risk to listed and non-listed terrestrial 

plants are considered possible based on ecological incident reports involving plants. Also lime 

sulfur is used to thin fruit and therefore can affect plants with abscission zones. 
22

7. Endocrine Disruptor Screening Program

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints, which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, and 

sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and chronic 

studies that assess growth, developmental and reproductive effects in different taxonomic groups. 

As part of registration review for lime sulfur, EPA reviewed these data and selected the most 

sensitive endpoints for relevant risk assessment scenarios from the existing hazard database. 

However, as required by FFDCA section 408(p), lime sulfur is subject to the endocrine screening 

part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide active 

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a 

“naturally occurring estrogen, or other such endocrine effects as the Administrator may designate.” 

The EDSP employs a two-tiered approach to making the statutorily required determinations. Tier 

1 consists of a battery of 11 screening assays to identify the potential of a chemical substance to 

interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go

through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal 

systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of 

the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any 

adverse endocrine-related effects caused by the substance, and establish a dose-response 

relationship between the dose and the E, A, or T effect.

Under FFDCA section 408(p), the EPA must screen all pesticide chemicals. Between October 

2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, 

which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of chemicals 

identified for EDSP screening was published on June 14, 20138 and includes some pesticides 

scheduled for registration review and chemicals found in water. Neither of these lists should be 

construed as a list of known or likely endocrine disruptors. Lime sulfur is not on List 1. For further 

information on the status of the EDSP, the policies and procedures, the lists of chemicals, future 

lists, the test guidelines and the Tier 1 screening battery, please visit our website.9

8. Endangered Species Assessments

In November 2013, the EPA, along with the U.S. Fish & Wildlife Service (USFWS), the National 

Marine Fisheries Service (NMFS) (collectively, the Services), and the U.S. Department of 

Agriculture (USDA) released a summary of their joint Interim Approaches for assessing risks to 

 8 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals. 9 http://www.epa.gov/endo/
23

listed species from pesticides. The Interim Approaches were developed jointly by the agencies in 

response to the National Academy of Sciences’ (NAS) recommendations and reflect a common 

approach to risk assessment shared by the agencies as a way of addressing scientific differences 

between the EPA and the Services. The NAS report outlines recommendations on specific 

scientific and technical issues related to the development of pesticide risk assessments that EPA 

and the Services must conduct in connection with their obligations under the Endangered Species 

Act (ESA) and FIFRA. 

The joint Interim Approaches were released prior to a stakeholder workshop held on November 

15, 2013. In addition, the EPA presented the joint Interim Approaches at the December 2013 

Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues Research and Evaluation 

Group (SFIREG) meetings, and held a stakeholder workshop in April 2014, allowing additional 

opportunities for stakeholders to comment on the Interim Approaches. As part of a phased, 

iterative process for developing the Interim Approaches, the agencies will also consider public 

comments on the Interim Approaches in connection with the development of upcoming 

Registration Review decisions. The details of the joint Interim Approaches are contained in 

the white paper “Interim Approaches for National-Level Pesticide Endangered Species Act 

Assessments Based on the Recommendations of the National Academy of Sciences April 2013 

Report,” dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the Interim 

Approaches to assess the potential risks of pesticides to listed species and their designated critical 

habitat, this preliminary risk assessment for lime sulfur does not contain a complete ESA analysis 

that includes effects determinations for specific listed species or designated critical habitat. 

Although EPA has not yet completed effects determinations for specific species or habitats, for 

this preliminary assessment EPA conducted a screening-level assessment for all taxa of non-target 

wildlife and plants that assumes for the sake of the assessment that listed species and designated 

critical habitats may be present in the vicinity of the application of lime sulfur. This screening level 

assessment will allow EPA to focus its future evaluations on the types of species where the 

potential for effects exists once the scientific methods being developed by the agencies have been 

fully vetted. 

This assessment for lime sulfur indicates potential risks of direct effects to listed freshwater fish

and invertebrates, birds, and mammals on an acute exposure basis. The potential for risk to listed 

and non-listed terrestrial plants exists as well due to observed phytotoxicity. Listed species of 

plant-dependent taxa may also be affected through indirect effects because of the potential for 

direct effects on listed and non-listed species upon which such species may rely. Potential direct 

effects on listed terrestrial plants from the use of lime sulfur may be associated with modification 

of Primary Constituent Elements (PCEs) of designated critical habitats, where such designations 

have been made. Once the agencies have fully developed and implemented the scientific methods 

necessary to complete risk assessments for endangered and threatened (listed) species and their 

designated critical habitats, these methods will be applied to subsequent analyses for lime sulfur 

as part of completing this registration review.
24

9. Risk Conclusions

Although the problem formulation of this assessment hypothesized that based on the most sensitive 

toxicity values, direct exposure to calcium polysulfides from their use as a fungicide/acracide may 

result in acute and chronic adverse effects to non-target aquatic and terrestrial organisms, the 

likelihood of direct acute exposure to the lime sulfur is considered low and the likelihood of 

chronic exposure is considered even more remote. The 2005 RED and 2015 new use assessments

concluded that based on the relatively rapid dissociation of lime sulfur to constituents that are 

routinely found in the environment and generally regarded as safe, the likelihood of adverse effects

on animals is low. The assessments also concluded that there is a low likelihood that elevated 

residues of potentially toxic constituents such as hydrogen sulfide will result in the environment 

from agricultural usage of lime sulfur, because the amount of sulfur added to the sulfur cycle from 

such uses does not substantially contribute to the pool of sulfur already present in reducing 

environments. While caustic intermediates (e.g., CaOH) can form as lime sulfur dissociates, 

elevated levels of these compounds are expected to be short-lived due to the natural buffering 

capacity of the soil/water. This current assessment has come to a similar conclusion.

This assessment evaluated the potential risks to terrestrial and aquatic animals and has concluded 

that the likelihood of acute and chronic exposure is low; therefore, likelihood of adverse effects on

these taxa is considered low. Although this assessment indicated potential risks of direct effects 

to freshwater fish on an acute exposure basis, application of calcium polysulfides to targeted 

foliage/soils and its movement to water bodies by drift is expected to result in low concentrations 

of calcium polysulfides in these systems. Such quantities are not believed likely to significantly 

alter natural background levels of these elements in the environment nor are they expected to 

substantially alter the pH of most receiving waters because of large dilution volumes and natural 

buffering capacity that is typically present. In a worst case scenario, the application of lime sulfur 

at the highest application rate would result in a decrease by 0.33 pH units. Such additions might 

potentially cause small alterations in the pH of a water body that has low buffering capacity; 

however, minor fluctuations in pH are not expected to have direct impact on the aquatic life 

contained therein. The use of oil formulations of lime sulfur is believed to further reduce the 

importance of drift as a transport pathway to water bodies. Similarly, for estuarine/marine systems, 

the likelihood of exposure is considered low, especially given the inherent buffering capacity of 

such systems; therefore, the likelihood of adverse effects on estuarine/marine organisms from the 

use of lime sulfur is considered low. Refer to Appendix A for additional information regarding 

alterations of pH in an aquatic system.

This assessment indicates potential risks of direct effects to listed birds and mammals on an acute

oral exposure basis. However, the likelihood that sufficient quantities of the material would 

remain on dietary forage items to represent a risk to birds or mammals on a subacute dietary 

exposure basis is considered low. Although EFED has no data to support the contention that 

neither birds or mammals would willingly consume caustic solutions of lime sulfur, the likelihood 

of this occurring is considered low. Although lime sulfur can move from application sites to 

adjacent lands via drift from treated areas, the material is expected to rapidly dissociate into mainly 

sulfur and calcium ions, which are not believed likely to substantially alter natural background 

levels of these elements in the environment. 
25

Although calcium polysulfides can be applied multiples times per year, due to the short half-life, 

multiple applications are not expected to result in accumulation of the parent compound on 

terrestrial forage items. Given the rapid dissipation, chronic exposure to calcium polysulfides is 

not expected. The use and application of calcium polysulfides are not expected to significantly 

increase the total calcium or sulfur content of soils and/or forage surfaces above background levels. 

In a worst case scenario, the application of lime sulfur on the terrestrial environment at the highest 

application rate will lower (acidify) acidic or neutral soils by less than 0.5 pH units. Refer to 

Appendix A for additional information regarding pH alterations in terrestrial environments.

Potential risks to terrestrial invertebrates is an uncertainty. On an acute contact exposure basis, 

lime sulfur is practically non-toxic to honey bees. The compound is not expected to persist in the 

environment and the extent to which it could be brought back to the colony to expose in-hive bees 

may be limited given the humid conditions which exist in honey bee colonies, since such 

conditions would likely promote the dissociation of the compound. There is anecdotal information 

to suggest that if bees are foraging at the time of application, they may be affected. Other beneficial 

insects though, that may be in their larval form, such as those reported in the effects 

characterization may be at risk if exposed at the maximum application rate. 

The use of lime sulfur may represent a potential for risk to listed and non-listed terrestrial plants

given that the compound can affect plant abscission and there are incident data to support concerns 

regarding phytotoxicity. Because of potential risks to terrestrial plants, secondary effects to plantdependent taxa may also occur. This uncertainty is amplified by the lack of terrestrial plant toxicity

data and could be reduced if such data were provided. 

10. Literature Cited

ATSDR. 2004. Agency of Toxic Substances and Disease Registry U.S. Department of Health 

and Human Services Public Health Service. Toxicological Profile for Hydrogen Sulfide. September 2004.

Atkinson, JD, Brian RM, Chamberlain EE, Cottier W, Dingley JM, Jacks H, Reid WD, Taylor GG. 1956. Plant 

Protection in New Zealand. Wellington, New Zealand: Government Printer, 699 pp.

Baird, C. Environmental Chemistry 2nd edition, W.H. Freeman and Company, New York\, NY. 

2003.

Balls PW and Liss PS. 1983. Exchange of H2S between water and air. Atmos. Environ. 17:735-

742.

Bartlett, B.R. 1964. The toxicity of some pesticide residues to adult Amblyseius hibisci, with a compilation of the 

effects of pesticides upon Phytoseiid mites. J. Econ. Entomol. 57(4):559-562.

Bartlett, B.R. 1966. Toxicity and acceptance of some pesticides fed to parasitic hymentoptera and predatory 

Conccinellids. J. Econ. Entomol. 59(5):1142-1149.

Elliot S and Rowland FS. 1990. The effect of metal complexation on the hydrogen sulfide 

transport across the sea-air interface. J. Atmos. Chem. 10:315-327.
26

Bodek, I.T, Lyman, W.J., Reehl, W.F., Rosenblatt, D.H. 1988. Environmental Inorganic Chemistry. Properties, 

Processes and Estimation Methods. Pergamon Press. New York, NY. PP 8.2-1 to 8.2-10.

Holb, IJ, DeJong PF, and Heijne B. 2003. Efficacy and phytotoxicity of lime sulphur in organic apple production. 

Ann. Appl. Biol. 142 (2): 225-233.

Elliot S and Rowland FS. 1990. The effect of metal complexation on the hydrogen sulfide transport across the sea-air 

interface. J. Atmos. Chem. 10:315-327.

James, D.G. and Rayner, M. 1995. Toxicity of viticultural pesticides to the predatory mites Amblyseius victoriensis 

and Typhlodromus doreenae. Plant Protection Quarterly 10(3):99-102.

Jørgensen BB. 1982. Ecology of the bacteria of the sulphur cycle with special reference to anoxic-oxic interface 

environments. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 298:543-561.

Llewelyn, FWM. 1965. The ‘hardening effect of lime-sulphur sprays on maiden apple trees. Ann. Appl. Biol. 

55:495-501.

McCann, J.A. 1976. Miller Lime Sulfur Solution: Acute Toxicity to Rainbow Trout: Test No. 1041. Biological 

Report of Analysis. U.S. Environmental Protection Agency, Pesticides Regulation Division, Animal 

Biology Section (Fish). unpublished report.

Shipton, PJ. 1969. Observations on the phytotoxicity and other effects of fungicides used on black currents. Plant 

Pathol. 18: 133-137.

Smith KA, Bremner JM, Tabatalag MA. 1973. Sorption of gaseous atmospheric pollutants by soils. Soil Sci.

116:313-319.

Tate, KG, Manktelow DW, Walker JT, and Stiefel H. 2000. Disease management in Hawke’s Bay Apple Orchards 

converting to organic production. New Zealand Plant Protection 53: 1-6.

Tomlin C. 1994. Pesticide Manual 10th edition. British Crop Protection Council. The Royal Society of Chemistry, 

Cambridge U.K.

USEPA, 1998. Guidance for Ecological Risk Assessment. Risk Assessment Forum. EPA/630/R-95/002F, April 

1998.

USEPA, 2002. Hydroxides Tolerance Reassessment Eligibility Decision (TRED). Federal Register:

July 24, 2002.

USEPA, 2005. Environmental Fate and Ecological Risk Assessment for the Reregistration Eligibility Decision 

Document (RED) of Calcium Polysulfides, a Fungicide/acaricide. DP Barcode: D313165. Date: October 4, 

2005.

USEPA, 2013 Environmental Fate and Effects Preliminary Risk Assessment for the Registration 

Review of Sulfur. From Melendez, J. and Sappington, K. to Gayoso, J.; Britton, C.; and Costello, K.

USEPA, 2015. Environmental Fate and Ecological Risk Assessment for Proposed Use of Calcium Polysulfide (Lime 

Sulfur Solution) on Apple Blossom Thinning. DP Barcode: D422723. Date: March 17, 2015.
27

11. Appendix A: The Sulfur Cycle

Sulfur is a natural component of the environment. In its elemental and oxidized forms, sulfur is 

estimated to represent 1.9% of the total weight of the earth. In soils and sediments, sulfur cycling 

involves the transformation of sulfur between its +6 and -2 oxidation states. These reactions are 

largely mediated by microorganisms. The reduction of sulfate to sulfide by microorganisms such 

as the sulfate reducing Desulfovibrio bacteria, occurs in virtually any anaerobic habitat containing 

organic matter and sulfates. Hydrogen sulfide is oxidized by chemosynthetic bacteria known as 

colorless sulfur bacteria, which oxidize sulfide in the presence of oxygen, and by photosynthetic 

green and purple bacteria. The oxidation of hydrogen sulfide to sulfate is also accomplished by 

Thiobaccilli bacteria (aerobic sulfide oxidizers). The critical nature of the microbial process is 

underscored by the fact that there is no known chemical reaction for the reduction of sulfur from 

its +6 oxidation state to its S-2 state at ambient temperature and pressure, and that 50-60% of global 

sulfur oxidation is estimated to occur through microbial processes.

Sulfur may be reduced to form hydrogen sulfide. In aqueous solution, hydrogen sulfide is a weak 

acid, exhibiting two acid dissociation constants. The first dissociation yields bisulfide anion (HS–

), 

and the second yields sulfide anion (S2–); the pKa values for each of these dissociations are 7.04 

and 11.96, respectively. At a pH of 7, the ratio of the concentration of aqueous hydrogen sulfide 

to bisulfate ion is approximately 1-to-1. As the pH increases above 7, the ratio of concentration of 

bisulfide ion to aqueous hydrogen sulfide increases. Only above pH 12 will the concentration of 

sulfide ion become significant (>50%). Hydrogen sulfide is usually not a long-lived chemical 

species in the environment. In soils and water, hydrogen sulfide reacts with iron and other 

transition metals to form insoluble sulfides; however, where iron levels are low H2S may 

accumulate to toxic levels (Bodek et al. 1988). Several species of soil, aquatic, and marine 

microorganisms oxidize hydrogen sulfide back to elemental sulfur or various sulfates, and its halftime in these environments usually ranges from 1 hour to several hours (Jørgensen 1982). 

Hydrogen sulfide evaporates readily from surface water, and the rate of evaporation depends on 

factors such as temperature, humidity, pH, depth of the water body, and the concentration of certain 

metal ions. Hydrogen sulfide will cross the air-water interface with kinetics similar to other 

unreactive gases, such as oxygen (O2), nitrogen (N2), and carbon dioxide (CO2), at pHs ≤ 6 (Balls 

and Liss 1983). Bisulfide and sulfide ions will form complexes with trace metal ions (i.e., Zn2+, 

Co2+, and Ni2+) found in seawater (Elliot and Rowland 1990). Ambient atmospheric levels of 

hydrogen sulfide from natural sources are reported to range from about 0.11 to 0.33 ppb (0.15 to 

0.46 μg/m3) (ATSDR 2004). 

Clay or organic matter may adsorb hydrogen sulfide, effectively acting as an environmental sink. 

Smith et al. (1973) determined the sorption characteristics of hydrogen sulfide to six air-dried and 

moist soils in a laboratory study. The capacities of soil samples to sorb hydrogen sulfide ranged 

from 15.4 to 65.2 mg/g soil for the air-dried soils, and from11.0 to 62.5 mg/g soil for the moist 

soils (50% of field capacity). Capacities and rates of sorption were not significantly affected by 

sterilization of the soil sample, indicating that soil microorganisms are not likely to be involved in 

the sorption process. The authors noted that these values, however, would not provide reliable 

estimates of the amounts of hydrogen sulfide that could be sorbed by soils under natural conditions, 

where the environmental fate of the sorbed hydrogen sulfide would have to be considered. Under 
Page 28 of 30

natural conditions, it is likely that some of the hydrogen sulfide would be oxidized to sulfate, which 

may be removed by leaching or taken up by plants. This, in turn, may make gas sorption sites 

available for additional sorption (Smith et al. 1973). 

Scenario in soil10

The worst case calculation for pH change in soil will be for soils that are acidic, neutral or 

contain no CaCO3 (i.e., minimal buffering capacity). For neutral and acidic soils, the addition of 

217 lbs of CaS5 is calculated to decrease pH (increase acidity) by 0.5 pH units in coarse textured 

soils (sands, loamy sands), and 0.2 pH units in fine textured soils (loams, clay loam, clay). 

The maximum application rate of CaS5/A is ~217 lbs a.i./A. Because there is 80% sulfur in the 

CaS5 (5 x 32=160 g/mol) the sulfur application rate is 173.6 lbs a.i./A.

Coarse Textured Soils (6 six inches deep soil)

In order to change the pH 0.5 unit; Use ratio where d1=pH unit change 

d1pH unit/352 lbs S/A=X/173.6 lbs S/A; Solve X=173.6/352 

Fine Textured Soils (6 six inches deep soil)

In order to change the pH 0.2 pH unit; Use ratio d1pH unit/1054 lbs S/A=X/173.6 lbs S/A; Solve 

X=173.6/1054

Assuming that there is no contribution from CaCO3 in soil (low buffering capacity), the 

concentrations of CaS5 needed to change the pH are a lot higher than the maximum annual 

application rate of sulfur.

Scenario in aqueous solution due to Spray Drift Alone9

The pH change due to spray drift deposition of sulfuric acid in the standard pond was assessed. 

The resulting concentrations were multiplied by 2 to account for the two acidic protons in 

H2SO4, and converted to a molarity basis (see page 22 for equations). Waters with low 

alkalinity (20 mg/L as CaCO3) were assumed to test the effect of added acidity on poorlybuffered habitats.

This process in the environment can be very complex, therefore for simplicity, it was assumed 

that the only species providing buffering capacity is bicarbonate (HCO3-), in a close system and 

the initial pH is 7. The amount of hydrogen ion (x) entering the pond was used to change the 

amount of HCO3

- (-x) and H2CO3 (+x) in the following equilibrium; given the pKa for H2CO3

as 6.37*:

 10 http://articles.extension.org/pages/13046/raising-soil-ph-and-soil-acidification 9 General Chemistry by Linus Pauling: Published April 1st 1988 by Dover Publications (first published June 8th 1970)
Page 29 of 30

[ ] [ ] [ ] [ ] [ ]

[ ] 4.55E 7

H CO

H HCO H CO H HCO

2 3

3

2 3 ⇔ + 3 = = −

+ −

+ − Ka Equation 1

At pH 7 (Equation 2), the ratio of bicarbonate ion [HCO3

-

] to carbonic acid [H2CO3] molarity is 

given by the ratio of the equilibrium constant Ka to the hydrogen ion [H+] concentration:

[ ] [ ]

[ ]

( )

( ) 4.55

1E - 7

4.55E - 7

H CO

HCO

H 2 3

3 = = =

−

+

Ka Equation 2

For a given alkalinity at pH 7, the amount of bicarbonate is 4.55 times the carbonic acid

concentration. Calculations using the maximum amount of lime sulfur that can reach the pond 

via spray drift (refer to page 17 for a detail discussion) ~120 μg/L, the molecular weight of CaS5

(200 g/mol) and the initial concentrations of bicarbonate (2.00E-4M) and carbonic acid (4.40E-4

M) were used to determine the final pH change when applying lime sulfur. 

Thus, at 20 mg/L alkalinity (lower end of surface water alkalinity range) and considering that for 

each sulfur entering the environment two protons are release to the environment.

The amount of H+ added by spray drift (x) is used to shift the equilibrium (used to change the 

amount of bicarbonate ion (-x) and carbonic acid (+x) in the equation); and compute the new pH 

by rearranging Equation 2: The amount of hydrogen ion (x) entering

[H+

] = Ka x {[H2CO3] / [HCO3

-

]} Equation 3

Thus, using Equation 311 and the values mentioned above, the pH in pond water can change from 

7.00 to 6.99. 

Table 1 Pond-water pH changes due to application of Lime sulfur*

Application 

Method

Low Water Alkalinity (20 mg/L) **

Initial pH Final pH

Aerial 7.00 6.99

*: The CRC Handbook of Chemistry and Physics. 69th Ed; p. D-163

**: Levels of 20-200 mg/L as CaCO3 are typical of fresh water. 

Assuming that there is low buffering capacity in pond water, the concentrations of CaS2 

needed to change the pH in water are a lot higher than the spray drift obtained using 

maximum annual application rate of lime sulfur.

 11 General Chemistry by Linus Pauling: Published April 1st 1988 by Dover Publications (first published June 8th 1970)
Page 30 of 30

Appendix B: Output from OPP Aggregate Incident Database for Lime Sulfur