~n~roe sct Pmmtiscn, Pestlcldes, 

and T* Sum 

Environmental Fate and Ecological Risk Assessment for the 

Registration of Iodomethane (Methyl Iodide) 
I. ENVIRONMENTAL RISK CONCLUSIONS 

Iodomethane is a short-lived chemical in the lower atmosphere and unlikely to reach the upper 

atmosphere to deplete the ozone layer. The estimated maximum concentration of iodomethane in air 

appears unlikely to pose an acute risk to birds and mammals. Short-term inhalation exposures of 

iodomethane are unlikely to pose chronic risk to birds and mammals. It also appears that no adverse 

effect on aquatic invertebrates or fish are likely because of low potential of runoff to the surface water 

bodies from the tarped post application sites of iodomethane. The environmental fate data, the 

residual contents in soils, and Tier I and I1 models estimated concentrations suggest that the adverse 

effect on ground water or surface water is highly unlikely due to iodomethane use. 

Iodomethane is proposed for use as an alternative pre-plant hmigant for methyl bromide in fields to 

be planted to tomatoes, strawberries, peppers, select ornamentals, turf, and re-plants of trees and 

vines. Low aMinity for sorption into the soil (KO, 34.8 L Kg-')and highvapor pressure (405.9 rnrn Hg) 

of iodomethane suggest that volatilization of iodomethane is the major route of dissipation. Available 

data indicate that there is 54 to 80% dissipation to the air even before the tarpaulin is removed. Once 

it volatilized, iodomethane degrades rapidly in the lower atmosphere via direct photolysis and lasts 

in the atmosphere less than twelve days, as compared with two years for methyl bromide. Therefore, 

iodomethane is unlikely to reach upper atmosphere to impact ozone layer. The estimated ozone 

depletion potential (ODP) for iodomethane is 0.029 as compared to 0.65 for methyl bromide. 

However, global uncertainty on volatilization rates, residence time in soil, photolytic degradation of 

iodomethane, and the removal of iodine radicals from troposphere means that the possibility of 

detrimental effects of iodomethane on ozone layer and a contribution to global warming can not be 

excluded. 

The primary route of iodomethane exposure of nontarget terrestrial animals will be inhalation. Direct 

flux of iodomethane in air was estimated using the Industrial Source Complex (ISC) dispersion 

model and monitoring data from iodomethane treated field. The estimated maximum concentration 

of iodomethane (0.987 ppm) at 242 lbs a.i./acre appears unlikely to pose an acute risk to birds and 

mammals (the maximum proposed application rate is 235 lbs a.i./acre). Iodomethane is a short-lived 

chemical in the atmosphere. Therefore, there is low potential for chronic risk to birds and mammals. 

It also appears that no adverse effect on aquatic invertebrates or fish are likely because of low 

potential to runoff from the tarped post application sites of iodomethane to the surface water bodies. 

Based upon Tier I1 PRZM/EXAMS estimated environmental concentrations (EECs) for surface 

water, no Levels-of-Concern (LOCs) for aquatic invertebrates or fish are exceeded. EFED also 

believes that the Henry's Law Constant of 5.23~-03atm-m3/mole (highly soluble and volatile) of 

iodomethane suggest that chronic exposures to the aquatic invertebrates and fish are not likely to 

occur. 

EFED is uncertain regarding the effects of this hmigant to terrestrial and semi-aquatic plants as well 

as aquatic plants. Tier I and Tier I1 plant data will enable EFED to complete the risk assessment of 

plants. However, based in part on a prior draft of a biological opinion from the United States Fish 

and Wildlife Service (USFWS) for tarped uses of methyl bromide, the Field and External Affairs 

Division (FEAD) does not presently have a concern for the proposed tarped uses of iodomethane and 

Page 2 of 37 
endangered species, including endangered plants. 

Based on environmental fate data, the residual contents in soils, and Tier I and I1 models estimated 

concentrations, EFED does not expect iodomethane to adversely impact ground water or surface 

water. Tier I1 PRZM/EXAMS for surface water and Tier I SCIGROW for ground water were used 

to estimate iodomethane concentrations. These concentrations are in nanograms per liter (ng/L), or 

parts per trillion. However, since this compound is very soluble in water, there is the possibility of 

leaching to ground water, if slicing or removal of the tarpaulin coincides with, or is followed soon 

by, a rain event. EFED recommends adding cautionary language to the label to prohibit the slicing 

or removal of the tarpaulin if it is raining or if rain is expected within 48 hours. 

Page 3 of 37 
IT. INTRODUCTION 

Methyl bromide is used extensively on a global basis as a pesticide against nematodes, weeds, 

insects, fungi, bacteria, and rodents. However, methyl bromide has been identified as a significant 

ozone depleting substance, resulting in regulatory actions being taken by the U.S. Environmental 

Protection Agency and by the United Nations Environment Program (Montreal Protocol). 

Iodomethane is proposed for use as an alternative pre-plant Iixnigant for methyl bromide in fields to 

be planted to tomatoes, strawberries, peppers, select ornamentals, turf, and re-plants of trees and 

vines. It is formulated as a 98% active ingredient (a.i.) product (TM-42501) with 2% chloropicrin 

as a "warning odorant", and a 25% a.i. product (TM-42503) with 75% chloropicrin as an active 

ingredient. The mode of action of monohalomethanes (chloride, bromide, iodide substituted) is still 

not well understood. The iodide ion concentration is insufficient to explain iodomethane toxicity. 

Toxicologic and metabolic similarities among the monohalomethanes suggest a common mechanism 

of toxic action, probably methylation and disturbance or inactivation of essential proteins. 

111. INTEGRATED ENVIRONMENTAL RISK CHARACTERIZATION 

Iodomethane, an alternative fumigant to methyl bromide, is a short-lived chemical in the lower 

atmosphere and unlikely reach the upper atmosphere to deplete the ozone layer. The environmental 

fate data, the residual contents in soils, and Tier I- and I1 model- estimated concentrations suggest 

that the adverse effect on ground water or surface water is highly unlikely due to iodomethane use. 

The estimated maximum concentration of iodomethane in air appears unlikely to pose an acute risk 

to birds and mammals. Short-term inhalation exposures of iodomethane are unlikely to pose chronic 

risk to birds and mammals. It also appears that no adverse effect on aquatic invertebrates or fish are 

likely because of low potential to runoff from the tarped post application sites of iodomethane to the 

surface water bodies. 

The high vapor pressure of 405.9 mm Hg at 25°C and Henry's Law constant of 5.23E-03atm-m3/mole 

and low affinity for sorption on soil (KO, 34.8 L Kg-') of iodomethane suggest that volatilization is 

the most important environmental route of dissipation. Field data fkom the applied iodomethane via 

broadcast shank injection in the bare-ground plot and followed simultaneously with a standard 1 mil 

plastic tarpaulin over the treated plot suggest that 54 to 80 percent of iodomethane was dissipated 

to the atmosphere even before the tarpaulin is removed. Once volatilized into the atmosphere, it 

degrades rapidly due to direct photolysis and the estimated atmospheric residence time is less than 

12 days. The estimated ODP iodomethane is less than 0.029, well below the level of Class I ozone 

depleters. Under Title VI, Section 602 of the Clean Air Act, the US Environmental Protection 

Agency classified any substance with an ODP 0.20 or greater as a Class I ozone depleting substance. 

However, global uncertainty on volatilization rates, residence time in soil, photolytic degradation of 

iodomethane, and the removal of iodine radicals from troposphere means that the possibility of 

detrimental effects of iodomethane on ozone layer and a contribution to global warming can not be 

excluded. 

Field dissipation data suggest that applied iodomethane was more confined to the soil layers adjacent 

to the 30-cm depth of iodomehane placement than the soil layers below 60 cm depth. No residual 

Page 4 of 37 
iodomethane was detected at the end of the field study period (90 days) at either site. Even if any 

iodomethane exposure should occur in the surface water, Henry's Law constant of 5.23E-03atmm3/mole suggests rapid volatilization of iodomethane to atmosphere. Tier I1 PRZMIEXAMS for 

surface water and Tier I SCIGROW for ground water were used to estimate iodomethane 

concentrations. These concentrations are in nanograms per liter (ng/L), or parts per trillion. Based 

on environmental fate, the residual contents in soils, and Tier I and I1 models estimated 

concentrations, EFED does not expect iodomethane to adversely impact ground water or surface 

water. 

Todomethane's use as a pre-plant fbmigant is not expected to pose a substantial direct risk to 

nontarget terrestrial or aquatic wildlife. It appears that the primary route of exposure of nontarget 

terrestrial organisms will be inhalation. Direct flux of iodomethane in air was estimated using the 

Industrial Source Complex (ISC) dispersion model and monitoring data from iodomethane treated 

field. Estimated data indicate that air concentrations of up to 0.987 ppm (at 30cm above the tarped 

ground at 8 - 19 hours post-application). Since the available avian acute inhalation LC50 is 395 pprn 

(over 400X this peak estimated residue), there does not appear to be a substantial risk of acute 

lethality to birds, even if they do fly above or land on the tarpaulin on the day of application. Birds 

off-site would be exposed to even lower residues and potential risk. 

It appears that mammals are less acutely sensitive than birds to iodomethane (LC50 equivalent to 689 

ppm). The HED recommended endpoint for human health risk assessment is an inhalation maternal 

NOAEL of 10 ppm in a developmental toxicity study, where rabbits were exposed for six hourslday 

for 23 days. The peak estimated short-term residues above the tarp (0.987 ppm) are below even this 

NOAEL from a 23-day study. Off-site or long-term residues and risk would be even lower. 

EFED does not consider iodomethane to pose an acute or chronic risk to fish and aquatic 

invertebrates because of low potential to runoff fiom the tarped post application sites of iodomethane 

to the surface water bodies. The low octanollwater partition coefficient (log KO, I 1.69) indicates 

that iodomethane is not likely to be bioconcentrated in tissues of aquatic organisms. The highest acute 

aquatic EEC for the iodomethane ecological risk assessment is 0.942 ppb, for Florida peppers. 

Comparing this value to the acute toxicity value (LC,,) for the most sensitive test species (D. magna, 

570 ppb) produces a maximum risk quotient of 0.0017. This is well below the lowest acute aquatic 

Level-of-Concern (LOC) of 0.05 (endangered species). EFED also believes that the Henry's Law 

Constant of 5 .23E-03atm-m3/mole (highly soluble and volatile) of iodomethane suggest that chronic 

exposures to the aquatic invertebrates and fish are not likely to occur. 

IV. ENVIRONMENTAL FATE ASSESSMENT 

(A) Physicochemical Properties 

Table 1 presents the important physical and chemical properties of iodomethane. The vapor pressure 

and Henry's Law constant are high, suggesting that volatilization is the most important environmental 

route of dissipation. Field volatilization studies (MRID 45593710 and 45593822) suggest that the 

concentrations of iodomethane in the fbmigated areas were significantly higher than the atmospheric 

Page 5 of 37 
background level (0.12 pg m-3 or 0.02 ppbv) during the 10-day monitoring period. Cumulative 

volatilization losses of iodomethane ranged from 54 to 94 percent within 10 days. The low 

octanol/water partition coefficient indicates that iodomethane is not likely to be bioconcentrated in 

tissues of aquatic organisms. 

Table 1. Physico-chemical and environmental fate properties of iodomethane. 

Phvsical and Chemical Properties 

Chemical Name 

- 

Iodomethane CAS No.74-88-4 

(Methyl Iodide, CH,I) 

Molecular weight 141.94 g/Mol MRID 45593705 

Water solubility 1420 mg/L at 25OC MRID 45593705 

Specific gravity 2.8 at 20°C Product Chemistry 

Vapor pressure 405.9 rnrn Hg at 25OC Product Chemistry 

Henry's law constant 5.23E-03 atm-m3/mole www.toxnet.nlm.nil.gov 

UV absorption Maximum (2.5 absorbance MRID 45593706 

units) at ca. 200 nm, with a 

smaller peak (0.25 au) at ca. 

250 nm 

OctanoVWater partition coefficient 1.5 1 - 1.69 

(1% KO,) 

Melting point 

International Occupational 

Safety and Health 

Information Centre 

International Occupational 

Safety and Health 

Information Centre 

Boiling point 42.4OC Product Chemistry 

Environmental Fate Pro~erties 

Hydrolysis Half-Life @ 

pH 4 @ 25oC 

pH 7 @ 250C 

pH 9 @ 250C 

Hydrolysis Half-Life @ 

pH 4 @ 500C 

pH 7 @ 500C 

pH 9 @ 500C 

MRID 45593705 

105 days 

94 days 

108 days 

3.4 days 

2.5 days 

2.6 day 

Page 6 of 37 
Table 1. Phvsico-chemical and environmental fate ~ro~erties of iodomethane. 

Aerobic Soil Metabolism t,, 2 hours (short half-life resulted MRTD 45593707 

due to volatilization of 

iodomethane) 

Anaerobic Soil Metabolism tIh, 38 hours (Sediment only) MRID 45593708 

Aerobic Aquatic Metabolism t,, 39 hours (Water only) MRID 45593708 

Anaerobic Aquatic Metabolism t,, 40 hours (Whole system) MRID 45593708 

Direct photolysis (atmosphere) 11.5 days1 D. Wuebbles, University of 

Illinois (personal 

communication, 2002) 

Direct Aqueous Photolysis 13 days MRID 45593706 

Soil Water Partition Coefficient 34.8 L Kg-' (SD k16.8) MRID 45593709 

(kc) (Mean of five soils) 

'Atmospheric model-estimated lifetime based on emissions globally distributed; lifetime will vary with location 

of emissions 

Conversion Factors 

To convert concentrations in air (at 25 "C) from ppm to mg/m3: mg/m3 = (ppm) molecular weight of the 

compound)/(24.45). For methyl iodide: 1 ppm = 5.8 1 mg/m3. 

To convert concentrations in air from pg/m3 to mg/m3: mg/m3 = (pg/m3) x (1 mg/1,000 pg). 

(B) Fate and Transport in soil and water 

The environmental fate data for iodomethane are also presented in Table 1. The rapid dissipation of 

iodomethane in both the aerobic soil (MRID 45593707) and anaerobic aquatic (MND 45593708) 

conditions is primarily the result ofvolatilization rather than microbial degradation. However, carbon 

dioxide was detected in both studies. It gradually increased to 1.1 percent of the total applied 

radioactivity by the end of the aerobic soil study and to 2.5 percent of the total applied radioactivity 

by the end of the anaerobic aquatic study. This indicates that limited microbial degradation of 

iodomethane may have affected soil aerobic and anaerobic metabolisms. Iodomethane was hydrolyzed 

slowly (94 to 108 days) in acidic, neutral, and alkaline conditions at ambient temperature yielding 16 

to 18 percent of methanol (MRID 45593705). Photolysis occurs both in gas and solution phases. The 

aqueous photolysis half-life for iodomethane in the irradiated solution was 13 days, based on the 

continuous irradiation used in the laboratory study (MRID 40593706). The major transformation 

products of aqueous photolysis were methanol and formaldehyde, which increased steadily to 

maximum concentrations of 18.7% and 36.5% respectively, after 15 days of irradiation. In batch 

equilibrium studies (MRID 45593709), iodomethane shows low absorption potential in five soils 

tested. The calculated Q,, , values ranged from 15-59 L ~g-l suggest that it has a high mobility in 

soil. In the field dissipation study (MRID 4559371 I), maximum iodomethane concentrations were 

4.157 mg a.i./kg (1.3 days) in the 15-30 cm soil depth, 2.677 mg a.i./kg (4 days) in the 30-45 cm soil 

Page 7 of 37 
depth, and 0.442 mg a.i./kg (4 days) in the 107-122 cm soil depth in California. Following the 

removal of tarpaulin, the plots were aerated through chiseling to facilitate the volatilization of residual 

iodomethane. The concentration of iodomethane below 122 cm was negligible (0.01 1 a.i./kg) at day 

8 post-treatment. At the Florida site, maximum iodomethane concentrations were 10.785 mg a.i./kg 

(0.3 days) in the 30-45 cm soil depth, 8.461 mg a.i./kg (1 day) in the 45-61 cm soil depth, and 0.209 

mg a.i./kg (14 days) in the 107-122 cm soil depth. Iodomethane was not detected at the end of the 

study period (90 days). Field dissipation data suggest that applied iodomethane was more confined 

to the layers adjacent to the 30 cm depth of iodomethane placement than soil layers below 60 cm. 

However, since this compound is soluble in water, there is the possibility of leaching through soil 

profile into ground water if removal or slicing of the tarpaulin coincides with, or is followed soon by, 

a rain event. 

(C) Fate and Transport in atmosphere 

Two field volatilization studies (MRID 45593 7 10 and 45593822) were conducted using iodomethane, 

which was applied via broadcast shank injection in the bare-ground plot and followed simultaneously 

with a standard 1 mil plastic tarpaulin over the treated plot. The volatilization of iodomethane (MRID 

45 593 7 10; methyl iodide; TM-425; technical; analytical purity 99.7%) was determined under field 

conditions on a sandy loam soil (41.6% sand content) in Watsonville, California and on a loamy sand 

(sand content 88.0%) soil in Dover, Florida. The sampling intervals for the study were inadequate 

to accurately establish the half-life ofthe test substance (> 50% ofthe test material degraded between 

the initial sample at day 0 and the second sample on day 1). 

Table 2. Time weighted average iodomethane (TM 425) residue at selected above ground heights 

in the center of the treated field in Manteca, California. 

3 -6 hours 

6-8 hours 

8- 19 hours 

NA = Not available 

Page 8 of 37 
Another field volatility study was conducted in a bareground plot of low organic matter containing 

sandy soil (sand content 9 1.0% ) located in Manteca, California (MRID 45 593 822). This study 

includes more frequent sampling intervals in the first 8 hours and the total mass of iodomethane lost 

from the soil was 94% ofthe applied (554 lb or 25 1 kg;) after 10 days. The greatest mass loss, 21%, 

occurred during the first three hours of application, while a mass loss of 4 1 % occurred within the first 

24 hours, and a 62% mass loss occurred within the first 2 days following application. Rapid diffisions 

of applied iodomethane through the tarpaulin suggest that the effectiveness ofthe tarpaulin to contain 

the applied hmigant may have been compromised. There was a slight increase in volatilization when 

the tarpaulin was cut open at day 4, but the recorded concentrations of iodornethane were well below 

the concentration on the application day. Table 2 shows the time-weighted average of iodomethane 

level at the center of the treated plot at various heights from the ground surface. These monitoring 

data in conjunction with time-averaged profiles of wind speed and air temperature were used to 

calculate the direct flux of iodomethane using ISC dispersion model. Flux rate decreased from 48 1 

yg/m2-s during the 3-hours following application, to 276 yg/m2-s at 3-6 hours, 87 Clg/m2-s at 6-8 

hours, and 48 pg/m2-sec at 8-19 hours on the application day (Table 3). In the first 12 hours of day 

1 (daytime), flux rate had increased to 115 yg/m2-sec, before decreasing to 17 CLg/rn2-sec at12-24 

hours (nighttime) of day 1. Results suggest that volatilization of iodomethane exhibited diurnal 

fluctuation, with daytime period flux rates greater than nighttime period flux rates. 

Table 3 also presents the estimated iodomethane air concentrations at two different heights from the 

ground surface at the center of the hmigated field in California. At a height of 30 cm, the estimated 

concentration of iodomethane in air was 921 ppbv (5345 yg/m3) in the first 3 hours after application, 

607 ppbv at 3-6 hours, 987 ppbv at 8 to 19 hours, an average of 347 on day 1, and 12 ppbv on day 

10. At a height of 80 cm, the concentration of iodomethane in air was 453 ppbv in the first 3 hours 

after application, 266 ppbv at 3-6 hours, 182 ppbv at 8 to 19 hours, an average of 102 ppbv on day 

1, and 5 ppbv on day 10. 

Table 3. Estimated direct flux and air concentrations of Iodomethane (TM 425) at selected above 

ground heights in the center of the treated field in Manteca, California. 

Day 0,O-3 hours 

Day 0, 3-6 hours 

Day 0,6-8 hours 

Day 0,s-19 hours 

Day 1,O-12 hours 

Day 1, 12 24 hours 

Day 2,O-12 hours 

Day 2, 12 24 hours 

481 

276 

87 

48 

115 

17 

34 

6 

Page 9 of 37 
Table 3. Estimated direct flux and air concentrations of Iodomethane (TM 425) at selected above 

ground heights in the center of the treated field in Manteca, California. 

Day 3,O-12 hours 

Day 3, 12 24 hours 

Day 4,O-12 hours 

Day 4, 12 24 hours 

Day 10,O-12 hours 

Day 10, 12 24 hours 

(D) Persistence 

The distribution and lifetime of CH31 in the atmosphere is a factor of the rate of emission and 

removal, and is important for determining the build-up of the chemical in the atmosphere. To 

determine the atmospheric lifetime of CH31, estimates of removal [UV absorption cross-section and 

reaction rate constant of hydroxl (OH)] were obtained from other studies (MRID 45593712). 

Assuming evenly distributed flux of CH31 with latitude, Don Wuebbles and colleagues at the 

University of Illinois obtained a model-calculated atmospheric lifetime for iodomethane of 1 1.5 days. 

The derived atmospheric lifetime will depend on where emissions occur, with a shorter lifetime 

derived for emissions in the tropics and a longer lifetime for emissions at high latitudes @on 

Wuebbles, Personal communication, 2002). Atkinson et al. (1997) reported that iodomethane will 

degrade in atmosphere through direct photolysis process, with a lifetime of 2.8 to 5.5 days, but this 

is based on a crude approach to estimating the atmospheric lifetime for such a short-lived gas 

(Wuebbles et al., 200 1). Iodomethane will be also photolyzed at slower rates with the hydroxyl (OH) 

radical with roughly an atmospheric half-life of about 117 to 220 days, based on atmospheric average 

concentration of OH radicals (Brown et al., 1990 and Atkinson et al., 1997). Again, actual lifetime 

will depend on location of the emissions for such a short-lived gas. 

As a substance with a short atmospheric lifetime, iodomethane falls into the same category as npropyl bromide which has an atmospheric lifetime of 19 days. 7he Montreal Protocol on Substances 

that Deplete the Ozone Layer to date has not called for the regulation or phase out of these 

substances. In turn, the EPA under its authority under the Clean Air Act has chosen to allow the 

production, import, and use of these substances. However, there is a disparity in the atmospheric 

lifetimes, and therefore ozone depletion potential, of these substances depending on where they are 

emitted. The impacts of short-lived substances emitted from the tropical latitudes, which happens 

to be the general location of developing countries, may actually prove to be consequential. In such 

an event, it is not clear that the Parties to the Montreal Protocol would require that a stricter set of 

rules apply to developing countries than to developed ones. Thus, even short-lived compounds that 

Page 10 of 37 
have minimal impact when emitted from the U. S., could be phased out due to policy considerations 

by the Parties. 

(E) Monitoring Data (Air) 

The United States Environmental Protection Agency has compiled ambient air monitoring data from 

several urban and suburban locations throughout the United States of America and calculated a mean 

concentration of iodomethane in ambient air of 0.02 ppbv during 1972-85. The global measurements 

of iodomethane show that it is uniformly distributed over the ocean, with a range of 0.5-1.0 ppbv 

(Rasmussen et al., 1982). Brodzinsky and Singh (1982) have also compiled 561 ambient air data 

from several urban and rural locations throughout the United States of America for a period of 1983 

to 1985. They reported a maximum of 0.08 ppbv with the median concentration of 0.004 ppbv of 

iodomethane. 

(F) Ozone Depletion Potential 

Methyl halide compounds (methyl bromide, methyl chloride, and methyl iodide) are very reactive 

agents when released into the atmosphere (Redeker et al., 2000). Ozone depletion can be caused by 

an increase in the concentration of halogen radicals (chlorine, bromine and iodine) in the stratosphere. 

Photodissociation of CH31 produces iodine radicals that can reach the stratosphere in two ways: CH31 

can drift into the stratosphere before photo- dissociation releases iodine radicals (Pathway A), or 

dissociation can occur in the troposphere and a fraction of the iodine radicals can be transported into 

the stratosphere (Pathway B). Because CH31 is short-lived in the atmosphere, pathway B is likely to 

be quite important because the iodine radicals will generally be released in the troposphere, rather 

than the stratosphere, where the ozone layer is located. If iodomethane andlor iodine transported to 

the stratosphere, all iodine became available for free radical chemistry and it has been calculated that 

at the altitudes between 15-20 krn the efficiency of iodine for ozone destruction is several folds 

greater than that of chlorine (Soloman et al., 1994; up to 800 times more effective according to recent 

modelling studies of Wuebbles et al., 200 1 .) 

To simulate the distribution of I,, the Atmospheric and Environmental Research's 2-dimensional 

chemical transport model (AER 2-D CTM) was used (MRID 45593712). The calculation assumes 

the soluble I, species released (HI, HOI and ION02) are subject to removal by the processes of 

washout or dry deposition in the troposphere, while the bulk of I, in the stratosphere is in the form 

of I and 10. Calculated standard washout rate, which has an average first-order removal lifetime of 

2 to 10 days, and a deposition velocity of 1 cmlsec. The empirical ODP can be defined by the 

following equation: 

ODPemp = ODP(trop) + ODP(stratA) + ODP(stratB) 

where 

ODP(trop) = ODP of in the troposphere due to I, accumulation, 

ODP (stratA) = ODP in the stratosphere due to I, that are delivered by pathway A, 

ODP(stratB) = ODP in the stratosphere due to I, that are delivered by pathway B. 

Page 11 of 37 
All of these pathways need to be considered in deriving the Ozone Depletion Potential for a shortlived gas like iodomethane. 

Reliable ODP values for CH31 are difficult to obtain directly from model calculations for two reasons: 

1) the model calculations show that the accumulation ofI, in the troposphere leads to ozone depletion 

in the troposphere, but the model is not capable of resolving variabilities in the troposphere on a 

regional scale, making the predicted results unreliable. 2) The models have not been tested to 

determine if they can accurately predict transport of short-lived source gases and their degradation 

products from the troposphere to the stratosphere. Nonetheless, the recent studies of Wuebbles and 

colleagues at the University of Illinois (personal communication, 2002) give an ODP for CH31 of 

0.029 assuming evenly distributed emissions with latitude. The ODP would be greater in the tropics 

and smaller than this at high latitudes. Only in the case of emissions in the tropics would there be an 

ODP approaching 0.1. Zhang et al. (1998) reported that the estimated ODP of iodomethane is less 

than 0.016, which is well below the 0.65 ODP for methyl bromide and the Class 1 listed ozone 

depleter compounds of the U. S. Environmental Protection Agency. Under Title VI, Section 602 of 

the Clean Air Act, the US Environmental Protection Agency classified any substance with an ODP 

0.2 or greater as Class 1 ozone depleting substance. However, this analysis would not have 

considered all of the pathways, and certainly did not consider that the ODP would be a fbnction of 

location of the emissions for such a short-lived gas ( Wuebbles et al., 2001). 

(G) Global Warming Potential 

Radiative forcing is the ability of a gas to absorb infrared radiation (within the atmospheric spectral 

window of 750cm-1 and 1300 cm-1), changing the balance of radiation absorbed or emitted by the 

atmosphere. A gas that strongly absorbs radiation in the atmospheric window, reduces the direct 

transmission of radiation emitted by the earth to space, enhancing the greenhouse effect (MRID 

45593712). 

One measure of the effectiveness of a gas to act as a greenhouse gas is the change in radiative forcing 

at the tropopause. Using the IR absorption cross-section derived from the absorption data from 

EPA7s Office of Air Quality Planning and Standards (Izttp://m.epa.ov/ttnl'emc/fiirirefcas.htmI), 

the AER 1-D RC model to calculate the radiative forcing for CH31, assuming that the concentration 

of CH31 in the stratosphere was zero. If the mixing ratio of CH31 decreased to 5% of its surface value 

at the tropopause, the radiative forcing was 2.8 x 10" Watt m-2 pbbv-' burden. Ifthe CH,I was wellmixed, the radiative forcing was 5.0 x 10" Watt m-2 per pbbv burden. For comparison purposes the 

radiative forcing for methane (CH,) and CH3Br were 5.0 x 1 Watt m-2 pbbv-' and 1.0 x 1 0-2 Watt 

m-2 pbbv-l, respectively. 

The radiative forcing results and a lifetime of 5.2 days were used to calculate the global warming 

potential (GWP) with different integration time horizons. In the case in which the mixing ratio of 

CH31 decreases to 5% of its surface value at the tropopause (radiative forcing is 2.8 x 10" Watt m-2 

pbbv-l), the GWP(20), GWP(100) and GWP(5OO) were calculated to be 0.06, 0.02, and 0.01, 

respectively. If CH31 is assumed to be well-mixed (radiative forcing is 5.0 x loq3 Watt m-2 pbbvql), 

Page 12 of 37 
the GWP(20), GWP(100) and GWP(5OO) were calculated to be 0.1 1, 0.03, and 0.01, respectively. 

The calculated values indicate that iodomethane may have negligible impact on greenhouse warming. 

V. WATER RESOURCE ASSESSMENT 

Rapid volatilization of iodomethane from water and soil surfaces is expected to be an important 

process due to a Henry's Law constant of 5.26E-03 atm-m3/mole. Field studies suggest that volatility 

yielded 54 to 80 percent of applied iodomethane even before tarpaulin was removed. Field dissipation 

data suggest that applied iodomethane was more confined to the soil horizons adjacent to the 30-cm 

depth of iodomethane placement. In California, hrnigated field was chiseled to aerate the site and 

enhanced the volatilization of residual iodomethane. Residual concentration of 1 0.01 1 mg a.i./kg on 

the day 8 and no iodomethane after 15 days were detected below one meter depth. In Florida, low 

residual concentrations of iodomethane of I 0.269 mg a.i./kg at day 7 and 10.034 mg a.i./kg at day 

28 were detected below one meter depth of the soil profile, which were higher than the California 

site. No residual iodomethane was detected at the end of the study period (90 days) in either site. 

Since this compound is very soluble in water and has low adsorption into soil, it can potentially leach 

into shallow ground water and leaky aquifers, especially when removal or slicing of the ground 

tarpaulin coincides with, or is followed soon by, a rain event. Tier I1 PRZMEXAMS for surface 

water and Tier I SCIGROW for ground water were used to estimate iodomethane concentrations 

(Table 4 and 5). Note that these concentrations are in nanograms per liter (ng/L), or parts per trillion. 

Based on environmental fate, the residual contents in soils, and Tier I and I1 models estimated 

concentrations, EFED does not expect iodomethane to adversely impact ground water or surface 

water. 

(B) Estimated Environment Concentration for Drinking Water Assessment 

The estimated drinking water concentrations (EDWCs) in surface waters derived from Tier I1 

PRZMEXAMS simulation employing Florida pepper index reservoir scenario and in ground waters 

calculated from SCIGROW are noted in Table 4. Since iodomethane is a volatile compound, 

additional input parameters like DAIR (vapor phase diffusion coefficient) and ENPY (enthalpy of 

vaporization) were activated during the PRZM-EXAMS simulation. The assessments were based on 

maximum application rate of iodomethane for pepper in Florida. A complete discussion of these 

models and the associated input parameters and output for each scenario is presented in Appendix 

A. These values generally represent upper-bound estimates of the concentrations that might be found 

in surface water and groundwater due to the use of iodomethane on pepper in Florida. 

Table 4. Tier I and I1 Estimated Drinking Water Concentrations of iodomethane 

Page 13 of 37 

Iodomethane 

ngn = PPt 

1965 6.7 60 
(B) Estimated Environment Concentration for Ecological Risk Assessment 

Estimated Environmental Concentrations (EECs) used to determine acute and chronic risks to aquatic 

organisms were estimated using tomato and pepper scenarios and Tier I1 PRZMEXAMS models. 

Since iodomethane is a volatile compound, additional input parameters like DAIR (vapor phase 

diflbsion coefficient) and ENPY (enthalpy ofvaporization) were activated during the PRZM-EXAMS 

simulation. 

Table 5. Tier I1 Estimated Environmental Concentrations of iodomethane 

California Tomato 1 242 1 1 / 383 1 140 1 29 1 10 

A complete discussion of these models and the associated input parameters and output for each 

scenario is presented in Appendix A. The maximum application rate (242 a.i. 1bsIA)for these crops 

and the relevant environmental fate parameters for iodomethane were used in PRZMEXAMS 

screening models. The EECs to be used for ecological risk assessments are presented in Table 5. 

Florida Pepper 

Monitoring Data (Surface water and Groundwater) 

Iodomethane has been detected in the surface water bodies. Naturally occurring iodomethane in sea 

water have been interpreted in terms of photochemical production mechanisms or in-situ synthesizing 

by marine organisms. Recent studies (Schall et al., 1994 and Nightingale et al., 1995) have 

demonstrated that marine organisms like phytoplankton and macro algae are capable of producing 

iodomethane in marine environments. Moore and Zafirou (1994) reported that the mean 

concentration of 1.6 ngll in the seawater samples from the eastern Pacific Ocean. At present time, 

iodomethane is not included in the Pesticides in Ground Water Database, National Water Quality 

Assessment Program (NAWQA) ofunited States Geological Survey (www.water.wr.usgs.gov), and 

it is also not included in the National Pesticide Survey. 

242 

VI. ECOLOGICAL HAZARD DATA 

(A) Summary 

1 

Available data indicate iodomethane is moderately toxic to birds (bobwhite quail) on both an acute 

oral and inhalation basis. It is highly toxic on an acute basis to freshwater invertebrates (Daphnia 

magna) and moderately toxic on an acute basis to fish (rainbow trout). 

Below is a presentation of the EPA's current iodomethane ecological toxicity data base. 

942 

Page 14 of 37 

224 43 15 
(B) Toxicity to Terrestrial Animals 

i. Birds, Acute and Subacute 

An acute oral toxicity study using the technical grade of the active ingredient (TGAI) is required to 

establish the toxicity of iodomethane to birds. The avian oral LD,, is an acute, single-dose laboratory 

study designed to estimate the quantity of toxicant required to cause 50% mortality in a test 

population of birds. The preferred test species is either the mallard duck, a waterfowl, or northern 

bobwhite quail, an upland gamebird. The TGAI is administered by oral intubation to adult birds, and 

the results are expressed as LD,, milligrams (mg) active ingredient (a.i.) per kilogram (kg). Toxicity 

category descriptions are the following: 

If the LD,, is less than 10 mg a.i./kg, then the test substance is ve7y highly toxic. 

If the LD,, is 10-to-50 mg a.i./kg, then the test substance is highly toxic. 

If the LD,, is 51-to-500 mg a.i./kg, then the test substance is moderately toxic. 

If the LD,, is 501-to-2,000 mg a.i./kg, then the test substance is slightly toxic. 

If the LD,, is greater than 2,000 mg a. i./kg, then the test substance is practically nontoxic. 

northern bobwhite quail 99.7 57 moderately toxic 45 593716fGallagher & Core 

(Colinus virginianus) Beavers1200 1 

' Core means study satisfies guideline. Supplemental means study is scientifically sound, but does not satisfy guideline. 

The guideline (71-la) is hlfilled (MRIDs 455937 16). 

Two dietary studies using the TGAI are usually required to establish the toxicity of pesticides to 

birds. However, given the volatility of iodomethane and its proposed use as a soil hmigant under 

ground that is immediately tarped, these studies are not needed at present for risk assessment. 

Because of the volatility of iodomethane, the registrant has submitted an avian inhalation study 

There is no established guideline (Subdivision E, 1982) for this test type. 

Table 8: Avian Acute Inhalation - Technical 

Northern Bobwhite Quail 99.7 395 moderately toxic 45593717/Kiplinger/2002 Supplemental 

(Colinus virginianus) (4-hr. exposure) 

Core means study satisfies guideline. Supplemental means study is scientifically sound, but does not satisfy guideline. 

Page 15 of 37 
While this study is considered scientifically sound, it is not a guideline study and thus is classified as 

Supplemental. Iodomethane is considered moderately toxic on an acute basis. 

(C) Toxicity to Freshwater Aquatic Animals 

i. Freshwater Fish, Acute 

Two freshwater fish toxicity studies using the TGAI are usually required to establish the toxicity of 

pesticides to fish. The preferred test species are rainbow trout (a coldwater fish) and bluegill sunfish 

(a warmwater fish). Results of one of these tests are listed below. The toxicity category descriptions 

for freshwater and estuarinelmarine fish and aquatic invertebrates, are defined below in parts per 

million (pprn). 

If the LC,, is less than 0. I pprn a. i., then the test substance is very highly toxic. 

If the LC,, is 0. I-to-I. 0 pprn a. i., then the test substance is highly toxic. 

If the LC,, is greater than I and up through 1 Oppm a. i., then the test substance is moderately toxic. 

If the LC,, is greater than 10 and up through I00 pprn a. i., then the test substance is slightly toxic. 

If the LC,, is greater than 100 pprn a. i., then the test substance is practically nontoxic. 

Rainbow Trout 99.7 1.331 (1.12-1.56) Moderately 45593714/Drottar, et. Core 

(Oncorhynchus sp.)/static-renewal toxic a1.12002 

With an LC,, of 1.33 ppm, iodomethane is categorized as moderately toxic to rainbow trout on an 

acute basis. The guideline for rainbow trout (72-lc) is hlfilled (45593714). A bluegill sunfish study 

is required for risk assessment and labeling. 

(ii) Freshwater Invertebrates, Acute 

A freshwater aquatic invertebrate toxicity test using the TGAI is required to establish the toxicity of 

iodomethane to aquatic invertebrates. The preferred test organism is Daphnza magna, but early instar 

arnphipods, stoneflies, mayflies, or midges may also be used. Results ofthis test are tabulated below. 

Table 10: Freshwater Invertebrate Acute Toxicitv - Iodomethane Technical 

Daphnid 99.7 0.571 (0.43-0.79) highly toxic 45593713lDrottar et. Core 

(Daphnia magna)lstatic- NOEC= 0.073 a1.1200 1 

renewal - - - - 

Core (study satisfies guideline). Supplemental (study is scientifically sound, but does not satisfy guideline). 

With an EC,, of 0.57 ppm, iodomethane is categorized as highly toxic to freshwater aquatic 

invertebrates on an acute basis. The guideline (72-2a) is hlfilled (MRID 450899 14). 

Page 16 of 37 
VII. AQUATIC EXPOSURE AND RISK ASSESSMENT 

The highest acute aquatic exposure estimate (EEC) for iodomethane presented in Table 5 above is 

0.942 ppb, for Florida peppers. Comparing this value to the acute toxicity value for the most 

sensitive test species (D. magna, 570 ppb) produces a maximum risk quotient of 0.0017. This is well 

below the lowest acute aquatic Level-of-Concern (LOC) of 0.05 (endangered species). Thus, EFED 

does not consider iodomethane to pose an acute risk to aquatic invertebrates or fish. EFED also 

believes that the Henry's Law Constant of 5.23E-03atm-m3/mole for iodomethane suggest that 

chronic exposures to the aquatic invertebrates and fish are not likely to occur. Although methanol 

and formaldehyde are major transformation products of aqueous photolysis of iodomethane, such 

transformation is expected to be minimal due to the primary route of dissipation to the air. 

VIII. TERRESTRIAL EXPOSURE AND RISK ASSESSMENT 

It appears that the principal risk to terrestrial wildlife will be from the inhalation of air residues near 

the treated sites. Estimated air concentrations are the highest on the application day, despite the 

mandatory tarping of treated sites. Estimated concentrations range up to 0.987 pprn at 30 cm above 

the tarp and up to 0.453 pprn at 80 cm above the tarp, based on submitted data. These values are 

estimated flux values based on cumulative charcoal tube residues collected following an application 

of 242 lb ailA (measured rate). This measured application rate is just above the proposed maximum 

label rate of 23 5 lb ailA. 

The avian acute inhalation LC,,, based on a four-hour exposure of bobwhite quail, is 395 ppm. Given 

that this is over 400X the peak estimated residues above, it does not appear that there is a substantial 

risk of acute lethality to birds, even if they do fly above or land on the tarp on the day of application. 

The lowest test concentration was 344 ppm, where sublethal effects were seen, including ataxia, 

gasping, and rales. Given that a No Effect Level was not obtained, it is not possible to say with 

certainty that there would be no sublethal effects at the expected maximum exposure levels above. 

However, given that the lowest test level was approximately 350X greater than the expected 

maximum residues, it is quite possible that there would be no sublethal effects as well. Iodomethane 

is also a short-lived chemical (direct photolysis, 11 1.5 days) in the atmosphere, therefore, there is 

low potential for chronic risk to birds and mammals. 

Because of dispersion and photolysis ofiodomethane, organisms offthe treated sites (e.g., birds, wild 

mammals) would likely be exposed to substantially lower residues and risk than those immediately 

above the tarp on the day of application. Mammals appear to be less acutely sensitive than birds to 

iodomethane. The reported mammal acute inhalation LC50 is 4.0 mgL (8112102 HED Memorandum; 

Appendix B), which is equivalent to 689 ppm. 

The HED recommended endpoint for human health risk assessment for all exposure time intervals 

is the inhalation maternal NOAEL in a developmental toxicity study with female New Zealand White 

rabbits, which is 10 pprn (8112102 HED Memorandum). This study included exposure of six 

hourslday on gestation days 6 through 28 (ibid.). It appears that 10 pprn is above acute wild mammal 

exposure and thus substantial risk is not expected. 

Page 17 of 37 
It is not expected that there would be any major use by wildlife of the soil under the tarp. However, 

some wildlife (e.g., amphibians) may possibly seek dark, warm, moist areas that such an area might 

provide. Any such use could possibly result in a lethal exposure, due to hrnigant concentrations. 

Guideline plant studies (seed germinationlseedling emergence, vegetative vigor, aquatic plant growth) 

are required to complete a risk assessment to plants. It is assumed, given the label reference to 

potential "...damage caused by drift to other plants or crops", that iodomethane could be hazardous 

to plants off-site. However, based in part on a prior draR biological opinion from USFWS for tarped 

uses of methyl bromide, the Field and External Affairs Division (FEAD) does not presently have a 

concern for the proposed tarped uses of iodomethane and endangered species, including endangered 

plants (3120103 note fkom A. Stavola, FEAD). 

Page 18 of 37 
REFERENCES 

Atkinson, R., D.L. Baulch, R.A. Cox, R.F. Hampson Jr., J.A. Kerr, M.J. Rossi, and J. Troe, (1997) 

Evaluated kinetic, photochemical and heterogeneous data for atmospheric chemistry. J. Phys. Chem. 

Ref. Data, 26 (3), 521 - 10 1 1. 

Brodzinsky R. and H.B. Singh. 1982. Volatile organic chemicals in atmosphere: an assessment of 

available data. SRI Intr Contract 68-02-3452. 

Brown, A.C., Canosa-Mas, C.E., R.P. Wayne. 1990. A kinetic study of the reactions of OH with 

CH31 and CF31. Atmospheric Environmental 24:36 1-367. 

Moore, R.M. and O.C. Zafirou. 1994. Photochemical production of methyl iodide in sea water. J. of 

Geophy. Res. 99: 16415-16420. 

Nightingale, P.D., Malin, G., and P.S. Liss. 1995. Production of CHC13 and other low molecular 

weight halocarbons by some species of macroalgae. Limnology and Oceanography 40:680-689. 

Rasmussen, R.A. Khalil, M.A.K., Gunawardena, R, and S .D. Hoyt. 1982. Atmospheric methyl iodide. 

J. of Geophy. Res. 87: 3086-3090. 

Redeker, K.R., N.Y. Wang, J.C. Low, A. Mcmillan, S.C. Tyler, R. J. Cicerone. 2000. Emissions of 

methyl halides and methane from rice paddies. Science 290: 966-979. 

Schall, C., F. Laturnus, and K.G. Heumann. 1994. Biogenic volatile organoiodine and organobromine 

compounds released from polar macroalgae. Chemosphere 28: 13 15-1324. 

Soloman, S., R.R. Garcia, and A.R. Ravishankara. 1994. On the role of iodine in ozone depletion. 

J. Geophy. Res. 99: 20491-20499. 

Wuebbles, D. J., K. 0. Patten, M. T. Johnson, and R. Kotamarthi. 2001. New methodology for 

Ozone Depletion Potentials of short-lived compounds: n-Propyl Bromide as an example. J. Geophys. 

Res., 106, 14551-14571. 

Zhang, W., M.E. McGiffen (Jr.), J. 0. Becker, H.O. Ohr, J. J. Sims, and S.D. Campbell. 1998. Effect 

of soil physical factors on methyl iodide and methyl bromide. Pestic. Sci. 53:71-79. 

Page 19 of 37 
Page 7 of 8 

- - -- 

, 

Table Al. Status of Environmental fate and ecological effect data requirements for iodomethane 

Date: May 08,2003 IODOMETHANE 

Case No: DATA REQUIREMENTS FOR THE 

Chemical No: 000011 ENVIRONMENTAL FATE AND EFFECTS DIVISION 

Data Requirements 

141-1 Honey Bee Acute 

Contact 

141-2 Honey Bee Residue 

on Foliage 

141-5 Field Test for 

Pollinators 

Composition1 

TGAI 

(TEP) 

5158.290 ENVIRONMENTAL FATE 

Degradation Studies-Lab: 

Use 

Pattern2 

1,2,3 

1,2,3 

1,2,3 

160-0 Global warming and 

ozone depletion potential 

161-1 Hydrolysis 

161 -2 Photolysis in Water 

161-3 Photolysis on Soil 

Does EPA Have 

Data To Satisfy 

This 

Requirement? 

(Yes, No, 

Partially) 

No 

No 

No 

TGAI 

TGAI 

TGAI 

TGAI 

Metabolism Studies-Lab: 

Bibliographic 

Citation 

Not applicable 

Not applicable 

Not applicable 

1,2,3 

1,2,3 

1,2,3 

1,2,3 

162-1 Aerobic Soil 

Metabolism 

162-2 Anaerobic Soil 

Metabolism 

162-3 Anaerobic Aquatic 

Metabolism 

162-4 Aerobic Aquatic 

Metabolism 

Study 

Classification 

Not applicable 

Not applicable 

Not applicable 

YES 

YES 

Partially 

Not applicable 

TGAI 

TGAI 

TGAI 

TGAI 

Additional 

Data Required 

Under FIFRA 

3(~)(2)(B)? 

NO' 

No 

No 

Mobility Studies: 

45593712 

45593705 

45593706 

Not Applicable 

1,2,3 

1,2,3 

1,2,3 

1, 2, 3 

163-1 Mobility (unaged) 

163-1 Mobility (aged) 

163-2 Laboratory volatility 

163-3 Field volatility 

Special 

Core 

Core 

Not Applicable 

YES 

YES 

YES 

YES 

TGAI 

TGAI 

TG AI 

No 

No 

No 

No 

Dissipation Studies-Field: 

45593707 

45593708 

45590708 

45590708 

1,2,3 

1,2,3 

1,2,3 

1,2,3 

164-1 Terrestrial field 

dissipation 

Core 

Core 

Core 

Core 

Partially 

No 

Not applicable 

YES 

TGAI 

No 

No 

No 

No 

Accumulation Studies: 

45593709 

Not applicable 

Not Applicable 

45593710 

1,2,3 

165-1 Fish 

bioaccumulation 

Core 

Not applicable 

Not Applicable 

Core 

YES 

1,2,3 

No 

No 

No 

No 

Ground Water Monitoring Studies: 

45593711 

Not Applicable 

166-1 Small scale 

prospective groundwater 

study. 

Core 

Not Applicable 

1,2,3 

No 

Not Applicable 

No 

No 

Not Applicable Not Applicable No 
1. Composition: TGAI=Technical grade of the active ingredient; PAIRA=Pure active ingredient, radiolabeled; TEP=Typical end-use product 

Table Al. Status of Environmental fate and ecological effect data requirements for iodomethane 

Date: May 08,2003 IODOMETHANE 

Case No: DATA REQUIREMENTS FOR THE 

Chemical No: 000011 ENVIRONMENTAL FATE AND EFFECTS DMSION 

2. Use Patterns: l=Terrestrial/Food; 2=TerrestriaVFeed; 3=Terrestrial Non-Food; 4=Aquatic Food; 5=Aquatic Non-Food (Outdoor); 6=Aquatic NonFood (Industrial); 7=Aquatic Non-Food (Residential); I=Greenhouse Food; 9=Greenhouse Non-Food; lO=Forestry, 1 l=Residential 

Outdoor; 12=Indoor Food; 13=Indoor Non-Food; 14=Indoor Medical; 15=Indoor Residential 

3. This study is not required due to the high volatility of iodomethane. 

Additional 

Data Required 

Under FIFRA 

3(~)(2)(B)? 

4. This study is required for risk assessment and labeling. 

Data Requirements 

5. At this time, available aquatic EECs are less than 0.01 of the lowest acute aquatic toxicity value and it does not appear that these studies will be needed. 

However, they are resewed pending any fhture EEC calculation andlor further analysis of aquatic exposure potential, as well as submission and review of the 

acute bluegill study. 

Bibliographic 

Citation 

$158.440 SPRAY DRIFT 

6. These studies are required since plants are among the target species and there are phytotoxicity warnings on the proposed labeling. 

Study 

Classification 

Does EPA Have 

Data To Satisfy 

This 

Requirement? 

Wes, No, 

Partially) 

Composition1 

NO 

NO 

Use 

Pattern2 

201-1 Droplet Size 

Spectrum 

202-1 Drift Field 

Evaluation 

Not Applicable 

Not Applicable 

Not Applicable 

Not Applicable 

1,2,3 

1,2,3 

NO 

NO 
APPENDIX A 

Modeling Inputs/Outputs for Ecological and Drinking Water Risk Assessment 

The maximum application rate and relevant environmental fate parameters for iodomethane were 

used in the two screening models PRZMIEXAMS and SCIGROW for iodomethane concentrations 

in surface water and groundwater, respectively. The outputs of the two screening models represent 

estimates of the concentrations that might be found in surface water and groundwater due to the use 

of iodomethane on selected crops. 

Estimation of surface water exposure concentrations for Ecological Risk Assessment 

The maximum application rate and relevant environmental fate parameters for iodomethane 

were used in the PRZMIEXAMS Tier I1 model for EECs in the surface water. The output of the 

screening model represent an upper-bound estimate of the concentrations of iodomethane that might 

be found in surface water due to use of iodomethane on selected crops. The weather, agricultural 

practices, and iodomethane applications were simulated over 30 years so that the ten year excedence 

probability at the site could be estimated. The EECs generated in this analysis were estimated using 

PRZM 3.12 (Pesticide Root Zone Model ) for simulating runoff and erosion from the agricultural 

field and EXAMS 2.98.5 (Exposure Analysis Modeling System) for estimating environmental fate 

and transport in surface water. Table A-1 summarizes the input values used in the selected crops and 

models run for PRZMIEXAMS. 

Estimation of Surface Water Exposure Concentrations for Drinking Water Assessment 

PRZMIEXAMS modeling using the Index Reservoir (IR) and the Percent Crop Area (PCA) 

adjustment was used to estimate concentrations in surface water used as a source of drinking water. 

The index reservoir represents a watershed that is more vulnerable than most used as drinking water 

sources. It was developed from a real watershed in western Illinois. The index reservoir is used as 

a standard watershed that is combined with local soils, weather, and cropping practices to represent 

a vulnerable watershed for each crop that could support a drinking water supply. If a community 

derives its drinking water from a large river, the estimated exposure would likely be higher than the 

actual exposure. Conversely, a community that derives its drinking water from smaller bodies of 

water with minimal outflow would likely get higher drinking water exposure than estimated using the 

index reservoir. Areas with a more humid climate that use a similar reservoir and golf coarse turf 

management practices would likely get more pesticides in their drinking water than predicted levels. 

A single steady flow has been used to represent the flow through the reservoir. Discharge 

from the reservoir also removes chemical from it so this assumption will underestimate removal from 

the reservoir during wet periods and overestimates removal during dry periods. This assumption can 

both underestimate or overestimate the concentration in the reservoir depending upon the annual 

precipitation pattern at the site. The index reservoir scenario uses the characteristic of a single soil 

to represent all soils in the basin. Soils can vary substantially across even small areas, thus, this 

variation is not reflected in these simulations. 

Page 20 of 37 
The index reservoir scenario does not consider tile drainage. Areas that are prone to 

substantial runoff are often tile drained. This may underestimate exposure, particularly on a chronic 

basis (the watershed on which the IR is based had no documented tile drainage). Additionally, 

EXAMS is unable to easily model spring and fall turnover which would result in complete mixing 

of a chemical through the water column during these events. Because of this inability, Shipman City 

Lake has been simulated without stratification. There is data to suggest that Shipman City Lake does 

stratify in the deepest parts of the lake at least in some years. This may result in both an over and 

underestimation of the concentration in drinking water depending upon the time of the year and the 

depth the drinking water intake is drawing fi-om. A full description of the Index Reservoir is provided 

in the "Guidance for Use of the Index Reservoir in Drinking Water Exposure Assessment" from 

EFED upon request. 

Development a Percent Crop Area (PCA), watershed-based adjustment factor for the percent 

of land in production for a specific crop, for Cherrylstone fruits has not been performed. The SAP 

recommended against the use of the PCA for 'minor7 crops because it believed that the scale of the 

watershed size used to develop the PCA (8-digit HUC) was too large to capture each drinking water 

watershed and the resulting PCAs would likely be highly inaccurate and not conservative (for the 

purpose of PCA development, cherrylstone fruits can be considered a minor crop). In the absence 

of a crop specific PCA, a default PCA of 0.87 is currently being used. 

The maximum application rate and relevant environmental fate parameters for cyprodinil were 

used in the PRZMEXAMS Tier I1 model for EDWCs in the surface water. The output of the 

screening model represent an upper-bound estimate of the concentrations of cyprodinil that might be 

found in surface water due to use of cyprodinil on Florida cabbage (Table A-6). The weather, 

agricultural practices, and cyprodinil applications were simulated over 30 years so that the ten year 

excedence probability at the site could be estimated. The EDWCs generated in this analysis were 

estimated using PRZM 3.12 (Pesticide Root Zone Model ) for simulating runoff and erosion fi-om the 

agricultural field and EXAMS 2.98.5 (Exposure Analysis Modeling System) for estimating 

environmental fate and transport in surface water. Table A-1 summarizes the input values used in the 

Florida cabbage and models run for PRZMIEXAMS. 

Table A-1. PRZMIEXAMS Input Parameters for Iodomethane 

I I 

Parameters ( Values & Units ( Sources 

Molecular Weight 141.94 g Mole'' Registrant Data 

Vapor Pressure 25°C 405.9 mm Hg @ 250C Product Chemistry 

Water Solubility @ pH 7.0 and 25°C 1420 mgL @ 250C MRID 45593705 

Henry's law constant 5 .26E-03atm-m3/mole www.toxnet.nlm.nil.gov 

Air Diffusion Coefficient 5345 cm21day Calculated 

Enthalpy of vaporization 20 kcallmol PRZM Standard 

Hydrolysis Half-Life (pH 7) 94 days MRID 45593705 

Aerobic Soil Metabolism t,, 0 .25dayst MRID 45593707$ 

Page 2 1 of 37 
Table A-1. PRZMIEXAMS In~ut Parameters for Iodomethane 

Direct Aqueous Photolysis 13.0 days MRID 45593706 

Soil Water Partition Coefficient 34.8 L Kg-' (Mean KO,) MRID 45593709 

CROP MANAGEMENT 

Parameters 

Florida Tomato 

Modeling scenario j Riviera Sand - MLRA 1564, Florida ................................................................................................................................... 

Culture type (Weed and moisture control) i Plastic Tarp ........................................................................ d .......................................................................................... 

Anaerobic- Aquatic metabolism: for entire 5.0 days? MRID 45593708t 

sedimentJwater system 

Values & Units 

Pesticide application frequency and rate 1 x 242.0 (lb a.i./A) Registrant Provided 

Sources 

Application Date 37694 Registrant Provided 

Application Method Ground Injection Registrant Provided 

Spray Efficiency 100% EFED 

Spray Drift None Standard assumption ................................................................................................................................................................. 

t = Input half-life was calculated from reported half-lives according to Guidance for selecting input parameters in modeling for environmental fate and 

transport of pesticides. Version 11. December 4,2001. 

Estimation of Ground Water Concentrations for Drinking Water Assessment 

SCIGROW is a regression-based model that provides a groundwater screening exposure value to be 

used in determining the potential risk to human health from drinking water contaminated with the 

pesticide. Since the SCI-GROW concentrations are likely to be approached in only very small 

percentage of drinking water sources (i.e. highly vulnerable aquifers), it is not appropriate to use SCIGROW for national or regional exposure estimates. 

SCIGROW estimates likely groundwater concentrations if the pesticide is used at the maximum 

allowable rate in areas where groundwater is exceptionally vulnerable to contamination. In most 

cases, a large majority of the use area will have groundwater that is less vulnerable to contamination 

than the areas used to derive the SCIGROW estimate. 

Table 2. SCIGROW Input Parameters for Iodomethane 

I I 

Parameters ( Values & Units I sources 

Aerobic Soil Metabolism t,,t 0.25days MRID 45593707% 

Soil Water Partition Coefficient 34.8 L Kg-' ................. (Mean K ) MRID 45593709 ............ oc ...................................................... 

Pesticide application ratelyear 1 x 242.0 (lb a.i./A) Registrant Provided 

Page 22 of 37 
Attachments 

(1) PRZMIEXAMS Model Output for Ecological Risk Assessment 

Florida Pepper 

Chemical: Iodomethane 

PRZM environment: FLpeppersC.txt 

EXAMS environment: pond298.e~ 

Metfile: w12844.dvf 

Application Method: Ground Injection 

Application Rate: 1X 242 ai. lbs/A 

Year Peak 

1961 0.00035 

1962 1.193-10 

1963 6.733-14 

1964 0.003237 

1965 6.353-25 

1966 3.953-19 

1967 3.223-16 

1968 0.1735 

1969 0.000863 

1970 4.053-11 

1971 9.153-27 

1972 1.833-18 

1973 6.953-13 

1974 41.98 

1975 3.403-23 

1976 4.323-40 

1977 0 

1978 0 

1979 0 

1980 9.223-22 

1981 0.000995 

1982 2.383-12 

1983 0.9544 

1984 7.083-09 

1985 1.623-06 

1986 1.843 

1987 0.8319 

1988 1.303-11 

1989 1.233-19 

1990 6.443-20 

Sorted results 

Prob. Peak 

0.03 41.98 

0.06 1.843 

0.10 0.9544 

0.13 0.8319 

0.16 0.1735 

Water segment concentrations (ppb) 

96 hr 21 Day 60 Day 90 Day 

0.00007 0.00001 0 0 

2.923-11 5.653-12 1.983-12 1.323-12 

1.713-14 3.383-15 1.183-15 7.893-16 

0.000686 0.000131 4.593-05 3.063-05 

5.883-25 3.333-25 1.403-25 9.393-26 

1.323-19 2.673-20 9.333-21 6.223-21 

1.023-16 2.053-17 7.173-18 4.783-18 

0.04365 0.008431 0.002951 0.001967 

0.000218 4.213-05 1.473-05 9.813-06 

9.253-12 1.773-12 6.213-13 4.143-13 

2.883-27 5.943-28 2.083-28 1.393-28 

5.523-19 1113-19 3.893-20 2.593-20 

1.663-13 3.253-14 1.143-14 7.593-15 

8.59 1 .642 0.5747 0.3831 

2.483-23 1.193-23 4.773-24 3.193-24 

3.993-40 2.343-40 1.013-40 6.733-41 

0 0 0 0 

0 0 0 0 

0 0 0 0 

2,813-22 5.643-23 1.983-23 1.323-23 

0.000232 4.463-05 1.563-05 1.043-05 

4.933-13 9.463-14 3.313-14 2.213-14 

0.2293 0.04415 0.01545 0.0103 

1.853-09 3.793-10 1.333-10 8.853-11 

3.513-07 6.713-08 2.353-08 1.573-08 

0.4628 0.08907 0.03118 0.02078 

0.1796 0.0344 0.01204 0.008026 

2.913-12 5.573-13 1.953-13 1.303-13 

3.693-20 7.423-21 2.603-21 1.733-21 

1.873-20 3.763-21 1.323-21 8.783-22 

96 hr 21 Day 60 Day 90 Day 

8.59 1.642 0.5747 0.3831 

0.4628 0.08907 0.03118 0.02078 

0.2293 0.04415 0.01545 0.0103 

0.1796 0.0344 0.01204 0.008026 

0.04365 0.008431 0.002951 0.001967 

Page 23 of 37 

Yearly 

7.993-07 

3.253-13 

1.953-16 

7.533-06 

2.323-26 

1.533-21 

1.183-18 

0.000484 

2.423-06 

1.023-13 

3.443-29 

6.383-21 

1.873-15 

0.09447 

7.873-25 

1.683-41 

0 

0 

0 

3.243-24 

2.573-06 

5.443-15 

0.00254 

2.183-11 

3.863-09 

0.005125 

0.001979 

3.203-14 

4.27000e-22 

2.163-22 

Yearly 

0.09447 

0.005125 

0.00254 

0.001979 

0.000484 
Inputs generaged by pe4.plAverage of yearly averages: 

.8-January-2003 

California Tomato 

Chemical: Iodomethane 

PRZM environment: CAtomatoC.txt 

EXAMS environment: pond298.e~ 

Metfile: w93 193. dvf 

Application Method: Ground Injection 

Application Rate: 1x242 a.i. lbs/A 

Year 

1961 

1962 

1963 

1964 

1965 

1966 

1967 

1968 

1969 

1970 

1971 

1972 

Water segment concentrations @pb) 

Peak 96 hr 21 Day 60 Day 90 Day Yearly 

3.903-17 2.603-17 7.50E-18 2.643-18 1.763-18 4.343-19 

1.673-16 7.633-17 1.813-17 6.333-18 4.223-18 1.043-18 

0.7684 0.2743 0.05596 0.01959 0.01306 0.00322 

1.583-18 1.343-18 8.733-19 4.453-19 3.053-19 7.533-20 

3.233-31 3.043-31 2.123-31 1.08331 7.36332 1.823-32 

0 0 0 0 0 0 

0 0 0 0 0 0 

0.0522 0.01742 0.003497 0.001224 0.000816 0.000201 

4.513-20 3.913-20 2.583-20 1.313-20 9.003-21 2.233-21 

1.24332 1.043-32 6.543-33 3.19333 2.173-33 5.373-34 

0 0 0 0 0 0 

0 0 0 0 0 0 

Page 24 of 37 
1973 

1974 

1975 

1976 

1977 

1978 

1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

Sorted results 

Prob. 

0.03 

0.06 

0.1 

0.13 

0.16 

0.19 

0.23 

0.26 

0.29 

0.32 

0.35 

0.39 

0.42 

0.45 

0.48 

0.52 

0.55 

0.58 

0.61 

0.65 

0.68 

0.71 

0.74 

0.77 

0.81 

0.84 

0.87 

0.90 

0.94 

0.97 

0.10 

Peak 

27.92 

0.7684 

0.3982 

0.2422 

0.0522 

0.01037 

0.000149 

1.643-11 

2.793-13 

7.803-14 

2.343-16 

1.673-16 

3.903-17 

1.583-18 

4.463-19 

4.513-20 

3.473-21 

4.253-23 

2.053-27 

2.483-29 

3.23331 

1.24332 

5.18335 

9.053-39 

1.403-42 

0 

0 

0 

0 

0 

0.3826 

21 Day 

1.632 

0.05596 

0.03016 

0.01776 

0.003497 

0.000883 

1.033-05 

1.113-12 

2.513-14 

7.243-15 

2.063-17 

1.81E-17 

7.503-18 

8.733-19 

4.063-20 

2.583-20 

2.353-21 

3.823-24 

1.193-27 

1.443-29 

2.12331 

6.54333 

2.713-35 

5.143-39 

1.403-42 

0 

0 

0 

0 

0 

0.02892 

Page 

60 Day 90 Day 

0.5714 0.3809 

0.01959 0.01306 

0.01056 0.007037 

0.006216 0.004144 

0.001224 0.000816 

0.000309 0.000206 

3.613-06 2.413-06 

3.883-13 2.593-13 

8-783-15 5.853-15 

2.533-15 1.693-15 

7.213-18 4.813-18 

6.333-18 4.223-18 

2.643-18 1.763-18 

4.453-19 3.053-19 

1.423-20 9.473-21 

1.313-20 9.003-21 

1.173-21 7.973-22 

1.343-24 8.913-25 

5.923-28 4.033-28 

7.213-30 4.923-30 

1.083-31 7.363-32 

3.193-33 2.173-33 

1.31335 8.92336 

2.60339 1.77339 

0 0 

0 0 

0 0 

0 0 

0 0 

0 0 

0.010126 0.006748 

Average of yearly averages: 

25 of 37 

Yearly 

0.09392 

0.00322 

0.001735 

0.001022 

0.000201 

5.083-05 

5.933-07 

6.383-14 

1.443-15 

4.173-16 

1.193-18 

1.043-18 

4.343-19 

7.533-20 

2.343-21 

2.233-21 

1.963-22 

2.203-25 

9.923-29 

1.223-30 

1.82332 

5.373-34 

2.203-36 

4.373-40 

0 

0 

0 

0 

0 

0 

0.001664 

0.003338 
(11) PRZMEXAMS Model Output for Drinking Water Assessment (Surface Water) 

Florida Pepper 

Chemical: Iodomethane 

PRZM environment: FLpeppersC.txt 

EXAMS environment: ir298.exv 

Metfile: w12844.dvf 

Application method: Ground Injection 

Application Rate: 242 a.i. lbs/A 

Water segment concent~ 

Year Peak 96 hr 21 Day 

1961 0.000839 0.000162 3.093-05 

1962 2.863-10 6.513-11 1.263-11 

1963 1.613-13 3.753-14 7.353-15 

1964 0.00776 0.001522 0.000291 

1965 9.263-25 8.533-25 4.863-25 

1966 9.473-19 2.983-19 5.963-20 

1967 7.713-16 2.313-16 4.603-17 

1968 0.4159 0.09522 0.01828 

1969 0.00207 0.000476 9.153-05 

1970 9.713-11 2.043-11 3.913-12 

1971 2.203-26 6.513-27 1.323-27 

1972 4.383-18 1.253-18 2.493-19 

1973 1.673-12 3.133-13 5.993-14 

1974 101 19.11 3.646 

1975 3.753-22 2.773-22 1.353-22 

1976 1.073-38 9.763-39 5.753-39 

1977 0 0 0 

1978 0 0 0 

1979 0 0 0 

1980 2.213-21 6.353-22 1.263-22 

1981 0.002387 0.000511 9.793-05 

1982 5.703-12 1.103-12 2.113-13 

1983 2.288 0.5027 0.09632 

1984 1.693-08 4.133-09 8.303-10 

1985 3.873-06 7.703-07 1.473-07 

1986 4.418 1.014 0.1943 

1987 1.995 0.4087 0.07813 

1988 ( 3113-11 6.513-12 1.253-12 

1989 2.963-19 8.383-20 1.673-20 

1990 1.543-19 4.323-20 8.603-21 

Sorted results 

Prob. Peak 96 hr 21 Day 

0.03 101 19.11 3.646 

0.06 4.418 1.014 0.1943 

0.10 2.288 0.5027 0.09632 

0.13 1.995 0.4087 0.07813 

0.16 0.4159 0.09522 0.01828 

0.19 0.00776 0.001522 0.000291 

0.23 0.002387 0.000511 9.793-05 

0.26 0.00207 0.000476 9.153-05 

-ations @pb) 

60 Day 

1.083-05 

4.393-12 

2.573-15 

0.000102 

2.073-25 

2.093-20 

1.613-17 

0.006398 

3.203-05 

1.373-12 

I 

4.633-28 

8.723-20 

2.103-14 

1.276 

5.473-23 

2.513-39 

0 

0 

0 

4.413-23 

3.433-05 

7.373-14 

0.03371 

2.913-10 

5.153-08 

0.06799 

0.02735 

4.373-13 

5.843-21 

3.013-21 

60 Day 

1.276 

0.06799 

0.03371 

0.02735 

0.006398 

0.000102 

3.433-05 

3.203-05 

90 Day 

7.213-06 

2.933-12 

1.723-15 

6.783-05 

1.393-25 

1.393-20 

1.073-17 

0.004265 

2.133-05 

9.113-13 

3.093-28 

5.813-20 

1.403-14 

0.8508 

3.663-23 

1.683-39 

0 

0 

0 

2.943-23 

2.283-05 

4.913-14 

0.02248 

1.943-10 

3.433-08 

0.04533 

0.01823 

2.913-13 

3.893-21 

2.013-21 

90 Day 

0.8508 

0.04533 

0.02248 

0.01823 

0.004265 

6.783-05 

2.283-05 

2.133-05 

Yearly 

1.783-06 

7.223-13 

4.233-16 

1.673-05 

3.423-26 

3.433-21 

2.643-18 

0.001049 

5.263-06 

2.253-13 

7.633-29 

1.433-20 

3.453-15 

0.2098 

9.033-24 

4.133-40 

0 

0 

0 

7.223-24 

5.633-06 

1.213-14 

0.005542 

4.763-11 

8.473-09 

0.01118 

0.004495 

7.163-14 

9.603-22 

4.953-22 

Yearly 

0.2098 

0.01118 

0.005542 

0.004495 

0.001049 

1.673-05 

5.633-06 

5.263-06 

Page 26 of 37 
Average of yearly averages: 

Inputs generaged by pe4.pl- 8-January-2003 

Estimated Drinking Water Concentration (EDWC) 

Acute EEC = (1110 peak value)( percent crop area) 

= ( 2259 ng/L)(0.87) =I965 ng/L 

Non-cancer Chronic EEC =(I110 yearly value)@ercent area area) 

(5.4 ng/L)(0.87) =4.70 ng/L 

Cancer chronic EEC = (Mean of annual value)@ercent crop area) 

(7.7 ng/L)(0.87) = 6.7 ng/L 

Page 27 of 37 
(III) SCIGROW Model Output for Drinking Water Assessment (Ground Water) 

RUN No. 1 FOR Iodomethane INPUT VALUES 

APPL (#/Ac) APPL. URATE SOIL SOIL AEROBIC 

RATE NO. (#/Ac/YR) KOC METABOLISM (DAYS) 

242.000 1 242.000 34.8 .25 

GROUND-WATER SCREENING CONCENTRATIONS IN PPB 

Page 28 of 37 
APPENDIX B 

TXR NO. 0051037 

DATE: August 12,2002 

MEMORANDUM 

SUBJECT: Iodomethane - Report of the Hazard Identification Assessment Review Committee. 

FROM: John E. Whalan, Toxicologist 

Registration Action Branch 2 

Health Effects Division (7509C) 

THROUGH: Jess Rowland, Co-Chair 

and 

Elizabeth Doyle, Co-Chair 

Hazard Identification Assessment Review Committee 

Health Effects Division (7509C) 

TO: Mary L. Waller, PM 12 

Registration Division (75 05 C) 

PC Code: 000011 

On July 30,2002, the Health Effects Division (HED) Hazard Identification Assessment Review Committee 

(HIARC) reviewed the recommendations of the toxicology reviewer for iodomethane with regard to the 

toxicological endpoint selection for use as appropriate in occupational and bystander risk assessments. The 

potential for increased susceptibility of infants and children from exposure to iodomethane was not 

considered because there will be no residue on food. The conclusions drawn at this meeting are presented 

in this report. 

Page 29 of 37 

-- .=#. ~wA *.- .- - - -- - - - ---- - 
Committee Members in Attendance 

Members present were: 

William Burnam 

Pamela Hurley 

Elizabeth Mendez 

John Liccione 

Jess Rowland 

Jonathan Chen 

Brenda Tarplee 

Member(s) in absentia: 

Elizabeth Doyle 

David Nixon 

Ayaad Assaad 

Steve Knizner 

Sue Makris 

Data evaluation prepared by: 

John E. Whalan, RAB2 

Also in attendance were: 

Alan Levy, RAE32 

Data Evaluation / Report Presentation -- 

John E. Whalan 

Toxicologist 

Page 30 of 37 

-- -- . - --- -- - - 
INTRODUCTION 

On July 30, 2002, the Health Effects Division (HED) Hazard Identification Assessment Review 

Committee (HIARC) reviewed the recommendations of the toxicology reviewer for iodomethane with 

regard to the toxicological endpoint selection for use as appropriate in occupational and bystander risk 

assessments. The potential for increased susceptibility of infants and children from exposure to 

iodomethane was not considered because there will be no residue on food. 

Iodomethane is a methyl bromide alternative that does not affect stratospheric ozone. Arvesta 

Corporation (formerly TomenAgro) has requested the registration of iodomethane as a pre-plant soil 

hmigant for use on strawberries and tomatoes to control soil-borne diseases, nematodes, and weed 

seeds. It can be injected into fields with the same equipment used for methyl bromide. Iodomethane has 

a higher boiling point than methyl bromide (42.5"C v 3.6"C), and one-fourth the vapor pressure (398 

mmHg v 1600 mmHg at 20°C). 

Names: 

Description: 

CAS #: 

Molecular Weight: 

Melting Point: 

Boiling Point: 

Vapor Pressure: 

Specific Gravity: 

TLV-TWA 

Structure: 

Iodomethane, methyl iodide 

Deep yellow, translucent liquid 

74-88-4 

141.95 g/Mol 

-66.5"C 

42.5"C 

398 mmHg 

2.28 at 20°C (2001 O ACGIH) 

2 ppm (12 mg/m3) 

I-CH, 

The toxic mode of action on target pests, laboratory animals, and humans is not known. Because there 

are no food residues in crops grown in treated soil, this is not a food use. Although there are no 

residential uses, homes and businesses adjacent to a treated field can be exposed to off-gassed 

iodomethane. Proposed iodomethane:chloropicrin formulations include 98:2, 50:50, and 25:75. 

Formulating with chloropicrin allows much less iodomethane to be used. 

I. FOPA HAZARD CONSIDERATIONS 

There are no FQPA considerations because iodomethane is a non-food use and there are no 

residential uses. 

1. Acute Reference Dose (am) - Because there are no food uses, an acute RfD was not 

established. 

2. Chronic Reference Dose (cRfD) - Because there are no food uses, a chronic RfD was not 

established. 

Page 3 1 of 37 
3. -sure: Short-Term (1-30 days) - There are no residential uses and no 

potential for exposure to infants or children, so an oral dose and toxicity endpoint were not 

selected. 

4. Incidental Oral Exposure: Intermediate-Term (1 - 6 Months) - There are no residential 

uses and no potential for exposure to infants or children, so an oral dose and toxicity endpoint 

were not selected. 

5. Dermal Absorption - Not applicable. 

6. Dermal Exposure: Short-Term (1- 30 davs) Exposure - The use pattern will not result in 

dermal exposure, so a dermal dose and toxicity endpoint were not selected. 

7. Dermal Exposure: Intermediate-Term (1 - 6 Months) - The use pattern will not result in 

dermal exposure, so a dermal dose and toxicity endpoint were not selected. 

8. Dermal Exposure Long-Term (> 6 Months) - The use pattern will not result in dermal 

exposure, so a dermal dose and toxicity endpoint were not selected. 

9. Inhalation Exposure: All-Time Intervals and All Populations 

Study Selected: Inhalation Developmental Toxicity Study in Rabbits fj870.3700 

MRID No.: 4559381 1 

Executive Summary: In a developmental toxicity study (h4RID 455938 1 1), groups of 24 female 

New Zealand White rabbits were dynamically exposed to iodomethane vapor (Lothatch # 

007403102; 99.6% a.i.) in whole-body inhalation chambers at analytical concentrations of 0, 2, 10, 

or 20 ppm (0, 0.012, 0.058, or 0.12 mgL1day) six hours per day on gestation days (GDs) 6 

through 28. All surviving does were sacrificed on GD 29, and their fetuses were removed by 

cesarean section and examined. 

No mortalities occurred during the study. When compared to concurrent controls, no treatmentrelated changes were observed in body weights, body weight gains, food consumption, sex ratios, 

or maternal gross pathology. 

At 20 ppm, an increased number of late resorptionsldoe were observed (1.6 treated vs. 0.1 

controls), which resulted in increased post-implantation loss in these animals (2.0 treated vs. 0.7 

controls). In addition, decreased (p<=0.05) gravid uterine weights were noted (decreased 3 1%). 

This decrease was attributed to decreased numbers of live fetusesldoe (decreased 41%) and 

decreased fetal weights (decreased 20%). Increased incidences of hair loss and wet, clear matting 

around the nose were noted in the 20 ppm animals compared to controls. Although these findings 

are of equivocal toxicological importance, they are evidence of nasal irritation. The postimplantation loss, decreased number of live fetuses, and decreased fetal weights may have been a 

consequence of subjecting the does to repeated respiratory irritation. 

Page 32 of 37 
The maternal LOAEL is 20 ppm (0.12 mg/l/day) based on post-implantation loss due to 

late resorptions, and a decreased number of live fetuses. The maternal NOAEL is 10 ppm 

(0.058 mg/l/day). 

The developmental toxicity LOAEL is 20 ppm (0.12 mgmday) based on decreased fetal 

weights (1 20%). The developmental toxicity NOAEL is 10 ppm (0.058 mg/l/day). 

DoseJEndpoint for Risk Assessment: The maternal NOAEL is 0.058 mg/l/day based on postimplantation loss due to late resorptions, and a decreased number of live fetuses at the LOAEL of 

0.12 mg/l/day. 

Comments about Studmndpoint: This endpoint should be used in risk assessments for all 

durations of human inhalation exposure. The following table demonstrates that the length of the 

inhalation toxicity study (from 1 to 90 days) has little effect on toxicity. The maternal NOAEL in 

the rabbit developmental toxicity study is about half that of the other NOAELs, possibly due to an 

idiosyncratic effect in rabbits. 

Study NOAEL LOAEL 

Acute neurotoxicity - rats 0.16 mg/L 0.54 mg/L 

Developmental toxicity - rats 0.12mg/L/day 0.35rngiLlday 

Developmental toxicity - rabbits 0.058 mg/l/day 0.12 mg/l/day 

13 -week toxicity - rats 0.12 mg/l/day 0.4 1 mg/l/day 

10. Margin - of Ex~osure 

The target Margin of Exposure (MOEs) for inhalation occupational and bystander exposure 

risk assessments is 100. 

11. Recommendation for Aggregate Exposure Risk Assessments 

Not applicable because there are no residential uses. 

III. CLASSIFICATION OF CARCINOGENIC POTENTIAL 

1. Combined Chronic Toxicity/Carcinoeenicity Study in Rats - This study is not required 

because iodomethane is a non-food use. 

2. Carcinogenicity Study in Mice - This study is not required because iodomethane is a nonfood use. 

3. Classification of Carcinogenic Potential - Carcinogenicity is not a concern because 

iodomethane will not have a food use, and there is no likelihood of long-term human exposure. 

IV. MUTAGENICITY 

Page 33 of 37 
Negative responses were observed in an Ames Assay, an in vitro mammalian cell mutation test in Chinese 

Hamster Ovary Cells, and in an in vivo micronucleus assay in mice. The only positive finding was in an in 

vitro chromosomal aberration test in Chinese Hamster Ovary in which there was induction of structural 

chromosome aberrations (clastogenesis). There was no induction of numerical aberrations in CHO cells, 

however. The HIARC concluded that there is no concern for mutagenicity resulting from exposure to 

iodomethane. 

V. HAZARD CHARACTERIZATION 

Toxicity Data Base Overview: The toxicity data base for iodomethane is limited because it has no food 

uses. The inhalation route has been well characterized, however, because this is the major route of 

worker exposure. The studies that have been submitted and reviewed include an battery of acute studies, 

an inhalation acute neurotoxicity study in rats, a 13-week inhalation toxicity study in rats, inhalation 

developmental toxicity studies in rats and rabbits, four mutagenicity studies, and a comparative oral v 

inhalation metabolism study in rats (not required by HED). These are all AcceptableIGuideline studies. 

There is a potential for accidental dermal exposure to iodomethane in workers due to a spill. Dermal 

exposure is expected to cause a rapid and persistent dermal response, but no systemic toxicity. No 

dermal toxicity studies were requested because the dermal dose cannot be quantified (iodomethane 

evaporates quickly from the skin), and there is no expectation of systemic toxicity. 

An inhalation 2-generation reproductive toxicity study was submitted, but was not reviewed due to 

regulatory time constraints and the fact that it is not needed for non-food-use registration. No chronic or 

carcinogenicity studies are required because iodomethane has no food uses, and there is no likelihood of 

long-term human exposure. 

Acute Toxicity: The Toxicity Categories for technical iodomethane are I for eye irritation, I1 for acute 

oral toxicity (in rats and mice) and skin irritation, I11 for acute dermal toxicity, and IV for acute inhalation 

toxicity. It is corrosive to the eyes with adverse signs persisting at 21 days, and is a severe skin irritant 

with rapid onset and effects persisting as much as 28 days. 

Pharmacokinetics and Cumulative Toxicity: A comparison of NOAELs and LOAELs demonstrates 

that the length of an inhalation toxicity study (from 1 to 90 days) has little effect on toxicity. This 

illustrates that there is minimal cumulation of iodomethane in the body. Although the maternal NOAEL 

in the rabbit developmental toxicity study is about half that of the other NOAELs, this is likely due to an 

idiosyncratic effect in rabbits (hypersensitivity to an irritant). 

Study NOAEL LOAEL 

Acute neurotoxicity - rats 0.16 mg/L 0.54 mg/L 

Developmental toxicity - rats 0.12 mg/L/day 0.3 5 mfllday 

Developmental toxicity - rabbits 0.05 8 mg/l/day 0.1 2 mg/l/day 

13-week toxicity - rats 0.12 mg/l/day 0.4 1 mgL/day 

A comparative oral v inhalation metabolism study (MRID 45641401) was performed in Sprague-Dawley 

rats using [14C] CH,I. Maximum blood concentrations were achieved within 4 hours (oral) and 0-2 hours 

Page 34 of 37 
(inhalation), and were proportional to dose/concentration. Initial t, was 5.1-7.2 hours, and terminal t, 

was 116-136 hours. 

Recovered radioactivity was primarily as CO, (39.40-60.81% dose) and in the urine (26.50-33.40% dose) 

in all treated groups, while feces accounted for <2% dose. Radioactivity remained in the carcasses 

(1 1.92-14.39% dose) of all treated animals 168 hours following treatment in the main test. Elimination 

t, were 17.8-22.3 hours for urine, 29.7-3 8.0 hours for feces, and 5.8-6.8 hours for CO, in all treatment 

groups. 

At 0-1 hour post-treatment in orally treated rats and 233 pprn inhalation exposed rats, relatively high 

levels of radioactivity were observed in the liver and GI tract. Radioactivity was relatively high in the 

kidney, lung, and nasal turbinates of the 25 pprn inhalation exposed rats and in the kidney, thyroid, and 

lung of the 233 pprn inhalation exposed rats. At 168 hours post-dose, radioactivity had declined in all 

tissues and was highest in the kidney, liver, and thyroid. Tissue concentrations increased (not 

proportionally) with dose. The major metabolites were expired CO,, and N-(methylthioacetyl) glycine 

and S-methyl glutathione which were excreted in the urine. Minor metabolites were methylthioacetic 

acid, methyl mercapturic acid, and S-methyl cysteine. 

Subchronic Toxicity: In a subchronic inhalation toxicity study (MRID 45593810), rats were 

dynamically exposed to iodomethane vapor for 6 hourslday, 5 dayslweek for 13 weeks at analytical 

concentrations of 0, 5, 21, or 70 pprn (0, 0.029, 0.12, or 0.41 mg/l/day). There were no effects on 

mortality, ophthalmology, urinalysis, hematology, organ weights, or gross pathology. The NOAEL is 21 

pprn (0.12 mg/l/day), and the LOAEL is 70 pprn (0.41 mg/l/day) based on initial decreases in body 

weights, body weight gains, and food consumption (males); and nasal degeneration. Respiratory 

irritation was observed at the interim (4 weeks) and terminal sacrifices. Microscopic findings indicated 

minimal to mild degenerationlregeneration of the nasal tissues characterized by subacute inflammation, 

respiratory epithelial metaplasia, degeneration, goblet cell hypertrophy, squamous cell hyperplasia, and 

minimal alveolar macrophages (females only). 

Developmental Toxicity: Female rats were dynamically exposed to iodomethane vapor in whole-body 

inhalation chambers at analytical concentrations of 0, 5, 20, or 60 pprn (0, 0.03, 0.12, or 0.35 mg/l/day) 

six hours per day on gestation days (GDs) 6 through 19 (MRID 45593812). No treatment-related 

changes were observed in clinical signs, the number of live and dead fetuses, resorptions, sex ratios, postimplantation losses, or maternal gross pathology. The maternal NOAEL is 20 pprn (0.12 mg/l/day), and 

the maternal LOAEL is 60 pprn (0.35 mgWday) based on decreased body weight gain (1 19%; 15-6% 

absolute body weight). Because no treatment-related developmental findings were noted at any 

concentration tested, the developmental NOAEL is 60 pprn (0.35 mgL1day). 

Female New Zealand White rabbits were dynamically exposed to iodomethane vapor in whole-body 

inhalation chambers at analytical concentrations of 0, 2, 10, or 20 pprn (0, 0.012, 0.058, or 0.12 

mg/l/day) six hours per day on gestation days (GDs) 6 through 28 (MRID 4559381 1). No treatmentrelated changes were observed in body weights, body weight gains, food consumption, sex ratios, or 

maternal gross pathology. The maternal NOAEL is 10 pprn (0.058 mgLIday), and the maternal LOAEL 

is 20 pprn (0.12 mglL/day) based on post-implantation loss (2.0 treated v 0.7 controls) due to late 

resorptions (1.6ltreated doe v 0. l/control doe), and a decreased number of live fetuses (1 41%). The 

post-implantation loss, decreased number of live fetuses, and decreased fetal weights may have been a 

consequence of subjecting the does to repeated respiratory irritation. The developmental NOAEL is 10 

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ppm (0.05 8 mg/l/day), and the developmental LOAEL is 20 ppm (0.12 mgL/day) based on decreased 

fetal weights ( 1 20%). 

Chronic ToxicitylCarcinogenicity and Mutagenicity: No chronic or carcinogenicity studies are 

required or have been submitted. Negative responses were observed in an Ames Assay (MRID 

45593813), an in vitro mammalian cell mutation test in Chinese Hamster Ovary Cells (MRID 45593815), 

and in an in vivo micronucleus assay in mice (MRID 45593816). The only positive finding was in an in 

vitro chromosomal aberration test in Chinese Hamster Ovary (MRID 45593814) in which there was 

induction of structural chromosome aberrations (clastogenesis), but no induction of numerical aberrations 

in CHO cells. The HIARC concluded that there is not a concern for mutagenicity resulting from 

exposure to iodomethane. 

Neurotoxicity: In an acute neurotoxicity study (MRID 45593817), rats were dynamically exposed to 

iodomethane vapor in a single, six-hour, whole body inhalation exposure at analytical concentrations of 0, 

27, 93, or 401 ppm (0,0.16, 0.54, or 2.3 mgL). The time of peak effect was estimated to be three hours 

post-exposure. The NOAEL is 27 ppm (0.16 ma). The LOAEL is 93 ppm (0.54 ma) based on FOB 

findings (clonic convulsions and decreased body temperature), and decreased motor activity (1 75-78% in 

males, 8 1-84% in females). 

Endocrinopathy: None of the animal studies provide any evidence that iodomethane disrupts endocrine 

receptors. 

VI. DATA GAPS I REOUIREMENTS 

There are no data gaps. 

VII. ACUTE TOXICITY 

Acut~ 

Acute Oral - rat 

Acute Oral - mouse 

11 870.1200 11 Acute Dermal 

1 870.1300 Acute Inhalation 1 870.2400 11 Primary Eye Irritation 

1 870.2500 11 Primary Skin Irritation 

11 870.2600 11 Dermal Sensitization 

Toxicity of Iodomethane 

45593808 I Severe irritant I I1 

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------- -- 

45593809 Negative - 
VIII. SUMMARY OF TOXICOLOGY ENDPOINT SELECTION 

Summary of Toxicology Endpoint Selection for Iodomethane 

Maternal LOAEL = 0.12 mg/L/day based on 

post-implantation loss due to late resorptions, 

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