UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, DC 20460 

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

PC Codes: 050507, 034902 

DP Barcode: 421836 

Date: August 19, 2014 

MEMORANDUM 

Subject: 

To: 

From: 

Registration Review Preliminary Risk Assessment for Ferric and Ferrous 

Sulfates 

Katherine St. Clair, Risk Manager Reviewer 

Cathryn Britton, Team Leader 

Kevin Costello, Branch Chief 

Risk Management and Implementation Branch 2 

Pesticide Re-Evaluation Division (7508P) 

Office of Pesticide Programs ..11 j 

61J ... 04/ \--

Edward Odenkirchen, Ph.D., Senior Science Ajvisor \ 9tl '{ 

Sujatha Sankula, Ph.D., Branch Chief A~ ~Ac S' l } 

Environmental Risk Branch 1 I~ =-

Environmental Fate and Effects Division (7507P) 

Office of Pesticide Programs 

The Environmental Fate and Effects Division (EFED) has completed a condensed preliminary 

risk assessment for ferrous and ferric sulfates in support of Registration Review. Discussion 

with the Pesticide Re-Evaluation Division risk managers lead to a condensed preliminary risk 

assessment approach that evaluated the risks in the context of past risk assessments supporting 

regulatory decisions and a determination if new uses or new data would alter the previous risk 

conclusions. This assessment relies on the previous Registration Eligibility Document (RED) 

for Iron Salts (http://www.epa.gov/oppsrrd 1/REDs/old reds/iron salt.pdf), the EFED 

Registration Review Problem Formulation for Ferrous Sulfate Monohydrate and Ferric Sulfate 

(Iron Salts) (D358772, http://www.regulations.gov/#!documentDetaii;D=EPA-HQ-OPP-2008-

0626-0004), and EFED's reviews of terrestrial plant seedling emergence and vegetative vigor 

studies categorized as supplemental for both chemicals (DP Barcodes: D399697, 400115, 

404679) and honeybee adult acute contact studies categorized as supplemental for limit tests, 

acceptable for the ferrous sulfate dose-response test and supplemental qualitative for the ferric 

sulfate dose-response test (DP Barcodes; D392671, 392679, 393680, 406105) submitted in 

response to the Registration Review Data Call-Ins 

(http://www.regulations.gov/#!documentDetaii;D=EPA-HQ-OPP-2008-0626-00 14 and 

http://www. regulations.gov/#!documentDetail:D=EP A-HQ-OPP-2008-0626-00 13 ). 
Background 

Iron is the fourth most abundant element and the second most abundant metal in the earth's 

crystal rocks. Iron occurs in a wide variety of minerals, and it is present in foods naturally and 

through added ingredients. 

Ferrous sulfate (or iron (II) sulfate, FeS04) is known as the monohydrate, FeS04·H20; the 

tetrahydrate, FeS04-4H20; the pentahydrate, FeS04·5H20; and the heptahydrate, 

FeS04 ·7H20. The heptahydrate is also called green vitriol, copperas, or melanterite (a mineral 

that commonly occurs with pyrite). It is a blue-green monoclinic crystalline water-soluble salt. 

It is prepared commercially by oxidation of pyrite (iron sulfide) or by treating iron with sulfuric 

acid. Ferrous sulfate monohydrate is a white, monoclinic, crystalline powder that occurs 

naturally as the mineral szomolnokite. Iron (II) sulfate is most commonly encountered as the 

blue-green heptahydrate. Iron (II) sulfate can be found in various states of hydration, and 

several of these forms exist in nature. 

• FeS04·H20 (mineral: szomolnokite) 

• FeS04·4 H20 

• FeS04 · 5 H20 (mineral: siderotil) 

• FeS04·7 H20 (mineral: melanterite) 

Ferric sulfate (or iron (III) sulfate, Fe2(S04)3) is a yellow rhombic crystalline hygroscopic water 

soluble salt that decomposes when heated to a temperature of 480°C. 

Iron salts are herbicides used primarily to control mosses. There are 16 products containing 

ferrous and ferric sulfates. For ferrous sulfate the end use products are formulated as a 

granular for terrestrial non-food and outdoor residential use ornamental herbaceous plants, 

lawns and turf, woody shrubs and vines. Ferrous sulfate is applied by hand or spreader at a 

single active ingredient rate of 1 to 4.7 lb/1 000 ft2. For ferric sulfate, the end use products are 

formulated as soluble concentrate/liquid (4.5-95.4% a.i.) for terrestrial nonfood use on 

ornamental lawns and turf and outdoor residential sites at a single active ingredient rate of 

0.74to 2.03 lb/1000 ft2. It is applied by sprinkler can and hose-end-sprayer. 

Previous RED and Current Registration Review Risk Conclusions for Terrestrial 

Vertebrates and Aquatic Taxa 

The RED evaluated the current lawn and turf uses of these two compounds for the control of 

moss. These uses include granules and hose-end or watering can applications. The RED 

indicated no risk concerns for the labeled uses of ferrous and ferric sulfates to terrestrial 

vertebrates or animals, and aquatic plants. A review of the Problem Formulation documents' 

listings of uses for the two chemicals and the summarized toxicological and environmental fate 

data indicate nothing has fundamentally changed since the completion of the RED risk 

assessment. Therefore, EFED concludes that the finding of no concerns for direct effects 

to terrestrial vertebrates or aquatic plants and animals found summarized in the RED 

still remains accurate. 

2 
Terrestrial Plant Risk Lines of Evidence and Conclusions 

The RED did not assess the risk to terrestrial plants for ferrous and ferric sulfates and plant 

studies were identified as data gaps in the Problem Formulation for both chemicals. The 

Environmental Fate and Effects Division (EFED) reviewed four Tier 1 screening terrestrial 

plant toxicity studies for ferrous sulfate (MRIDs 48650801, 4888050 I) and ferric sulfate 

(MRIDs 4873880 I, 487340 I) in support of Registration Review. The terrestrial plant studies 

were considered to provide sufficient information to support a Registration Review risk 

assessment but were classified as supplemental owing to the fact that they could not 

demonstrate a NOEC in all tested species. A current understanding of the use patterns for the 

two chemicals shows that uses are confined to watered in (watering can or hose end sprayer) 

and granular applications to lawns and turf. These application scenarios are not over the top 

spray applications so spray drift loading to adjacent areas to the use site is not expected. 

Moreover, EFED does not expect that runoff loadings will be significant to any degree because 

the compounds are expected to ionize and any resultant iron runoff is expected to be 

exceedingly low, ca. 4 X I 0-7 mg/L, and largely masked by natural iron background 

(communication between James Hetrick Senior Science Advisor, USEPNOPP/EFED/ERB3 

and Meghan Radtke, Risk Assessment Process Leader USEPNOPP/EFED/ERBl, June 9, 

2014). Consequently no complete exposure pathway, drift or runoff, of the applied ferric 

sulfate or ferrous sulfate is expected to off-site plants. 

In light of this understanding of the exposure pathways for non-target plants, EFED 

concludes that there are no concerns for direct effects to terrestrial plants. 

Pollinators and Terrestrial Invertebrates Risk Assessment and Conclusions 

Toxicity of Compounds to Honey Bees (and by surrogacy other terrestrial invertebrates) 

The RED did not assess the risk to terrestrial arthropods and pollinators for ferrous and ferric 

sulfates and honeybee effects studies (the surrogate species for pollinator and arthropods risk 

assessment) were identified as data gaps in the Problem Formulation for both chemicals. 

A total of four honeybee studies were submitted to EPA for review. Two studies were limit 

studies with ferric sulfate (MRID 48548701) and ferrous sulfate (MRID 48549601) that 

· demonstrated mortality to bees at the limit of25 ug ai/bee. These were classified supplemental. 

Two dose response studies were submitted to the Agency, reviewed and found to be acceptable 

for ferrous sulfate for quantitative use and supplemental for qualitative use for ferric sulfate; the 

later finding with ferric sulfate owing to a split dosing design that limits the statistical 

confidence in the results: 

• Acute Contact-Dose response study ferric sulfate (MRID 48935401, supplemental qualitative): 96-h LDso 

235 uglbee 

• Acute Contact-Dose response study ferrous sulfate (MRID 4857860 I, acceptable): 96-h LDsa >I 00 

uglbee; NOEL I 00 uglbee 

3 
Exposure Assessment/or Bees (and other terrestrial invertebrates by analogy) 

EFED employed the following contact exposure assessment model from available policy: 

Honey bee adult contact exposure ug/bee = (application rate lb/acre) (2.7) 

Maximum residues in treated areas receive pesticide treatment were estimated using this model 

as follows: 

• Ferric sulfate 

Maximum application 2.03 lbs/1 000 ft2 

= 90.2 lbs/acre X 2. 7 = 244 ug/bee 

• Ferrous sulfate 

Maximum application 4.675 lbs/1 000 ft2 

= 203.6 lbs/acre X 2.7 =550 ug/bee 

Bee Comparison ofToxicity Values to Exposure Estimates (and screening level assessment for 

other terrestrial invertebrates) 

The ratio of exposure to available effects information for honeybees is as follows for the two 

compounds: 

• Ferric sulfate (presumptive ratio as effect values cannot provide a definitive quantitative 

endpoint due to statistical limitations) 

244 ug/bee exposure level exceeds effect estimate of235 ug/bee by a factor of 1.04 

• Ferrous sulfate (presumptive ratio as RQs cannot be definitively established without 

LDso) 

550 ug/bee exposure level exceeds effect estimate by less than a factor of 5.5 

Bee Risk Characterization (limited analogy for individuals of other terrestrial invertebrate 

species) 

In neither case can the uncertain ratios provided above be directly compared with the Agency 

Level of Concern (LOC) for acute honeybee risks of 0.4 or greater. However in both cases it 

appears that exposure levels are in excess of the best available estimates available for lethal 

toxicity. There is possible concern for bees directly contacted by spray applications on lawns 

and turf if attractive flowering plants are also present. However, given the herbicidal nature of 

ferric sulfate, the likely low attraction of moss for honeybees, and an expectation that the lawn 

and turf uses are targeted to small treatment areas, any given application of the compound is 

not likely to result in hive impacts. 

The ferrous sulfate exposures exceed the maximum tested level by a factor of five; however, 

this value was shown to produce no adverse effects at this concentration. Because exposures to 

ferrous sulfate are so much higher than the NOEC it is not possible to definitively establish the 

risk concerns. However, consideration of the supplemental acute limit study with honey bees 

in which 48% of the tested bees died at an exposure of25 ug/bee (MRID 48549601) would 

suggest that acute effects are possible though the observation of mortality in the limit study is 

4 
confounded by high mortality in the controls, suggesting that the 48% figure might be 

overinflated. If one assumed that ferrous sulfate was roughly equivalent to ferric sulfate in bee 

toxicity (i.e.,~200 to 300 ug/bee for an LDso), there still would be concerns that exposures in 

the field would exceed acute toxicity thresholds. These toxicity considerations combined with 

a low attraction of moss to bees, the herbicidal effects of iron salts to bee attractive plants 

preventing bee attraction, and the expected limited geographic extent for any given application 

of the compound, any possible bee effects would be incidental and not likely to result in hive 

impacts. 

Concerns for ferric sulfate effects on individual honey bees contacting sprayed areas is weakly 

supported by the available data. Multiple lines of evidence would suggest that both compounds 

may lethally affect bees in treated areas. Consideration of the uncertain effects thresholds, 

the low attraction of target mossy areas for bees, and the expected low geographic extent 

for any given application of the compounds applied to the intended use areas would 

suggest that any putative bee effects would not rise to a level where hives would be 

impacted. 

Potential for Effects to Federally Listed (Threatened and Endangered) Species. 

Consistent with the RED and without any additional information, EFED finds no direct effect 

risk concerns for listed and non-listed terrestrial vertebrates or any aquatic organisms. A 

reevaluation of the nature of the uses of ferric and ferrous sulfates suggests that exposure 

pathways to off-site vegetation are inconsequential and so there are no concerns for direct 

effects to non-target terrestrial plants. Therefore, this risk assessment indicates that there 

are no effects to Federally listed terrestrial vertebrates and plants and aquatic organisms 

associated with the registration of ferric and ferrous sulfates in accordance with existing 

labels. 

The available data on effects to honey bees would suggest localized acute effects are possible. 

Many of the limiting risk factors in the honeybee assessment are transferable to a risk 

characterization for lethal impacts: highly uncertain lethality to tested invertebrates, low 

attractiveness of the target areas, and low geographical extent of treatment. Considering these 

lines of evidence along with an absence of spray rift and no appreciable runoff, the immediate 

area of application to moss, on residential and turf areas, constitutes a very limited geographical 

extent of exposure (the materials are applied by watering can or hose end sprayer). It is not 

reasonable to assume that listed invertebrate species will be in the immediate proximity of these 

application sites and so effects are not reasonably expected to occur for Federally listed 

terrestrial invertebrates. 

5 
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