MEMORANDUM 

SUBJECT: 

FROM: 

THRU: TO: 

Review of Sulfonyl Urea (SU) Plant Reproduction Studies 

Elizabeth Riley, Co-chair, Plant Technical Team (PTT) 

Robin Sternberg, Co-chair, PTT 

Nancy Andrews, Management Representative, PTT 

Environmental Fate and Effects Division 

Donald Brady, Division Director 

Environmental Fate and Effects Division (7507P) 

Michael Goodis, Associate Division Director Pesticide Re-evaluation Division (7508P) 

In the past, the Agency has had concerns that sulfonylurea (SU) herbicides may have effects on 

plant reproduction at rates lower than those that cause visual phytotoxic effects to vegetative 

vigor (i.e., growth). These concerns were highlighted in the Registration Eligibility Decision 

[RED] for chlorsulfuron (D330621) and sulfometuron-methyl (D354292). As a result of the 

uncertainties associated with reproductive effects, a Data-Call-In (DCI) for plant reproduction 

studies was issued for these chemicals. Information from open literature sources available at that 

time was reviewed and reported. However, a comprehensive review of the potential for 

reproductive effects at rates relative to effects on vegetative vigor had not been conducted. As 

additional SUs entered the registration review process, and additional plant reproduction studies 

were requested, a thorough review of the available information became a high priority. 

Additionally, the chlorsulfuron DCI study was submitted to the Agency for review. 

As a result of this priority, the PTT was tasked with conducting a review of the available 

information in order to determine whether there is sufficient information to support the risk 

hypothesis that exposure to SU herbicides during reproductively active life-stages will result in more sensitive endpoints than exposure during vegetatively active life-stages. 

The PTT has finalized a comprehensive review of the available registrant-submitted and open 

literature plant reproduction studies conducted with SU herbicides (described in further detail in 

the Supporting Documentation section below). This review focused on the comparison of effects 
in Problem Formulations for the SU herbicides: 

EFED's Plant Technical Team (PTT) conducted an analysis of available SU plant reproduction 

data from the open literature and the registrant-submitted data for chlorsulfuron and concluded 

that data .from the 850.4150 vegetative vigor guideline study are sufficiently protective of 

potential impacts to plant reproduction. Acetolactate synthase (ALS) inhibitors primarily affect 

metabolically-active meristem tissues. When plants are exposed at a young, vigorously growing 

life-stage, effects are expressed primarily as inhibition of vegetative growth (i.e. biomass, shoot 

length). As plants mature these effects are less pronounced. However, as plants enter their 

reproductive life-stage, the metabolically-active tissue will include flower and seed production. 

Plants exposed to SU herbicides during the reproductive life stage are likely to exhibit adverse 

effects on reproduction, generally expressed as reduced seed number or reduced seed weight. 

Based on the latest data analysis, these effects are expected to occur at similar concentrations to 

those effects determined in the guideline vegetative vigor studies (850.4150) so further data are 

not requested at this time. 

Supporting Documentation 

Summary of Registrant Submitted Data 

E. I. DuPont De Nemours & Company has submitted several studies to evaluate the effects of 

chlorsulfuron applied at various crop growth stages. Effects from both vegetative and 

reproductive exposure on growth and yield responses (MRID 48776902) and seed viability 

(MRID 48776903) of soybean grown under greenhouse conditions are the studies considered 

most relevant to address the risk hypothesis. These studies indicate that soybean is no more 

sensitive to chlorsulfuron applied at the reproductive stage of growth than at the vegetative 

growth stage. These special studies confirm that the endpoint determined in the guideline 

vegetative vigor study for chlorsulfuron is protective of the inhibitory effects of exposure at 

reproductive stages. 

Summary of Open Literature Data 

In addition to the aforementioned review of the DuPont study, PTT conducted a thorough review 

of the available open literature plant reproduction studies. Table 1 provides a summary of the 

relevant information from each study that was used to compare the vegetative and reproductive 

endpoints. For reference, the associated regulatory endpoint from the guideline study is provided 

where available. For this comparison, a vegetative growth endpoint (e.g., height, weight, or 
1. A vegetative or reproductive endpoint was not provided in the study. 

2. Endpoint(s) was non-definitive (i.e., greater than or less than value). 

3. The vegetative growth endpoint was based on phytotoxic effects only. Many of the 

studies utilized some form of plant injury index based on semi-quantitative observations 

of phytotoxicity. Since plant height and dry weight can be more sensitive than 

observations of phytotoxicity, these endpoints do not reduce uncertainty as to whether 

reproductive effects may occur at levels below vegetative growth effects. 

4. Several studies exposed plants during the vegetatively active life-stage (e.g., the 2-, 4-, or 

6-leafstage) and measured vegetative growth and reproductive endpoints post flowering. 

These studies provide information that suggests plants exposed to SU herbicides during 

the vegetative vigor life-stage may experience lingering effects on reproduction; 

however, they do not address the question before the PTT. 

Although a majority of the open literature studies did not allow for direct comparison between 

vegetative growth and reproductive endpoints, there were seven studies that appear to address the risk hypothesis directly and were amenable to comparison across endpoints. For each of these 

studies, plants were exposed during either the vegetative or reproductive stages, vegetative data 

were collected in a manner consistent with guideline studies, and IC2s values were reported for 

the most sensitive vegetative (e.g., height) and reproductive (e.g., seed weight) endpoints. Data 

for three of these studies indicated that reproductive endpoints are equivalent to vegetative 

endpoints, whereas results from three studies suggest that the vegetative endpoints are less 

sensitive but within a factor of 3 of the reproductive endpoints. Given the variability associated 

with plant studies, endpoints within a factor of 3 of each other are not considered substantially 

different. Data from one study (Olszyk et al. 2009), however, did suggest that reproductive 

endpoints are two orders of magnitude more sensitive than vegetative endpoints when peas were 

exposed to sulfometuron-methyl. Since the results of this study were in sharp contrast to the 

results of the remaining studies, PTT requested the raw data from the study authors to conduct a 

more thorough review, as discussed in the following section. 
Table 1. C om 1ar1son o fSUR, duction Stud· 

' Vegeg.tive 

' Growth' Reproductive Regulatory Study, addresses risk 

€hemical, Species* IC1sl End{loint Endpoint (R) VG >R? Endp,oint** hypothesis1 andl is amenable Reference (Reference)f NOAE€ ~G) (lb a,i./A) (lb a.i./A) to comparison across 

I Ob a.i./A) endpoints? 

Registrant-Submitted Studies 

IC25 

2.34x1o-' 9.55 x1o-' 

Yes, VG conducted the same MRIDs 

Chlorsulfuron Soybean (1.36 x10-5

- (5 .24 x10-5

- No 280 x10-5 48776902 and (C. I.) 4.04 x10-5

) 17.31 x10-5

) as guideline. 48776903 

Open Literature Studies 

No, plants treated at 4- to 6-

Black NOAEC 2.0 x10-5 2.0 x10-5 No NR leaf stage. Measurements MRID 48915011 bindweed taken at 3 1 days post 

treatment. 

No, VG not conducted the 

Canola NOAEC 4.0 xl0-5 2.0 x10-5 Yes 0.9 x10-5 same as guideline. Treatment MRID 48915009 

at reproductive stage only. 

Chlorsulfuron Cherry NOAEC NR 4.0 x10-5 NP NR No, VG endpoints not MRID 48915006 reported. 

No, endpoints non-definitive. 

Foxtail NOAEC < 9.0x10-3 < 9.0x10-3 NP NR VG endpoints based on visual MRID 48915010 

injury index only. 

No, VG measurements for 

post-emergence application 

Pea NOAEC NR 8.0 x10-5 NP 72.0 x10-5 not reported. R endpoint based MRID 48915005 

on mean yield less than 75% 

of control. 

No, VG not conducted the 

Pea NOAEC 2.0 x104 0.08 x104 Yes 7.20 x104 same as guideline. Treatment MRID 48915008 at 6-leaf stage with visible 

flower buds. 

Chlorsulfuron No, VG not conducted the 

Soybean NOAEC 2.0 x1o-s 2.0 x10-5 No 14.0 x10-5 same as guideline. Treatment MRID 48915009 

at reproductive stage only. 

No, VG not conducted the 

Sunflower NOAEC 2.0 xlo-5 4.0 xl0-5 No NR same as VV. Treatment at MRID 48915009 

reproductive stage only. 

Smartweed NOAEC < 2.0 xlo-~ < 2.0 xlo-~ No NR No, endpoints non-defmitive, MRID 48915009 
Table 1. C om ~ariSOD 0 fSUR duction Stud· 

Vegetative Study addresses risk Growth Reproductive ' Regulatory Chemical Species* :IC2s/ Endpoint Endpoint (R) VG>R? Endpoint** hypothesis and is amenable Reference (Reference) NOAEC (V~) (lb a.i./A) (lb a.i./A) to comparison across 

(lb a.i./A) endpoints? 

VG not conducted the same as 

guideline. Treatment at 

reproductive stage only. 

Yes (by No, VG endpoints based on 

Sweet NOAEC 2.0 xl0-4 0.7xl0-4 order of NR visual injury index only. MRID 48915006 cherry magnitude) Application to mature tree 

branches. 

Metsulfuron Foxtail NOAEC < 9.0 xl0"3 < 9.0 xl0"3 

No, endpoints non-definitive. 

NP NR VG endpoints based on visual MRID 48915010 

injury index only. 

Nicosulfuron Soybean NOAEC 1.0 xl0·3 4.0 xl0·3 No NR No, VG not conducted the MRID 48915004 

same as guideline. 

Pea IC25 6.0 xl0-4 1.2 xl0-4 Yes (within NR Yes, VG conducted the same MRID 48915012 (S.E.) (2.0 xl0-4) (2.0 xl0-4) factor of2) as guideline. 

No, R endpoint not reported. 

Primisulfuron Soybean NOAEC 4.0xl0-4 NR NP NR VG not conducted the same as MRID 48915004 

guideline. 

IC25 3.9 xl0-4 No, R endpoint not reported. 

Potato (S.E.) (2.0 xl0-4) NR NP NR VG conducted the same as MRID 48915001 . 

guideline. I 

IC25 

1.5 xl0-4 0.8 xl0-4 Yes (within Yes, VG conducted the same Study I 

(0.5 xl0-4- (0.2 xl0-4- 2.4lxl0-4 raw data from (C.I.) 4.6 xl0-4) 3.6 xl0-4) factor of2) as guideline. MRID 48915012 

Pea IC25 

6.0 xlo-~ 2.0 xto·~ Yes (within Yes, VG conducted the same Study2 

(2.0 xto·5

- (0.4 xto·5

- 24.1 xi0-5 

raw data from (C.I.) 36 xl0-5

) 8.0 xl0"5

) factor of3) as guideline. MRID 48915012 Sulfometuron IC25 9.0 xto·' 3.0 xlO"' Yes (within Yes, VG conducted the same 

(S.E.) (20 xl0-5

) (2.0 xl0-5

) factor of3) 24.1 xto·5 

as guideline. MRID 48915002 

Potato IC25 0.07 xlo-~ 3.0 xto·~ No NR Yes, VG conducted the same MRID 4891500 I (S.E.) (0.08 xi0-3

) (5.0 xl0-3

) as guideline. 

Soybean IC25 2.0 xl0-4 2.0 xl0-4 No 0.000018 Yes, VG conducted the same MRID 48915002 (S.E.) (2.0 xl0-4) (2.0 xl0-4) as guideline. 

Thifensulfuron Canota IC25 0.0005 NR NP 0.000048 No, R endpoints not reported. Wall, eta/., 1995 
Table 1. C om ~ar1son o fSUR, duction Stud' 

I Vegetative 

I Study address~ risk I I l€i&st GrowtbJ Reproductive Regulatory I 

€hemical ' Species* Endpoint Endp~int (iR) VG.>R? Endpoint** hy,pothesis and. is1 amenable 

~eference) I Reference 

r I NO.AEC' tvG~ @b a.i./A)l @ba.UA) to•comparison across 

I 1 (tb a.tJA), I endp"oints? 

IC25 calculated for fresh and 

dry weight. VG conducted 

similarly to guideline. 

No, VG measurements for 

Pea NOAEC NR 5.0 xl0-4 NP 9.8 xl0-4 

post emergence application 

not reported. R endpoint based MRID 48915005 

on mean yield less than 75% 

of control. 

No, R endpoint not reported. 

Canol a IC2s l.Oxl0-4 NR NP 1.0 xl0-4 IC2s calculated for fresh and Wall, eta/., 1995 dry weight. VG conducted 

similarly to guideline. 

Tribenuron 

No, endpoints non-definitive. Foxtail NOAEC < 9.0 xto·3 < 9.0 xl0"3 NP NR VG endpoints based on visual MRID 48915010 

injury index only. 

IC2s 2.0 xl0"5 No, R endpoint not reported. 

Potato (S.E.) (1.0 xl0"5

) NR NP NR VG conducted the same as MRID 4891500 I 

guideline. 

NR = value not reported; C.l. = confidence interval; S.E. = standard error 

NP = comparison is not possible either because a VG orR endpoint was not provided or because endpoints are less than or greater than values that do not allow 

for direct comparison 

*Scientific names for the tested species are: soybean (Glycine max), black bindweed (Polygonum convolvulus), canola (Brassica napus), cherry (Prunus avium), 

foxtail (Setaria spp.), pea (Pisum sativum), sunflower (Helianthus annuus), smartweed (Polygonum persicaria), and potato (Solanum tuberosum). 

**Comparable endpoint from the guideline study. 
p

y

The primary author ofthe study, David Olszyk ofORD's Western Ecology Division, provided 

the raw data which allowed the PTT to analyze the data in a manner consistent with standard 

EFED practice. For each study, the effect on 21-day plant height, the only vegetative vigor 

endpoint that was similar to 850.4150, was analyzed for plants exposed at the vegetative vigor 

stage to obtain ICzs values. In addition, the effect on seed weight, the most sensitive 

reproduction endpoint, was analyzed for plants exposed at the onset of the reproductive life-stage 

to obtain ICzs values. This analysis allowed the PTT to make direct comparisons between the 

effect of exposure timing on the most sensitive endpoints for each life-stage and address the 

research question of whether our current guideline study (i.e., vegetative vigor) is sufficiently 

protective of effects seen at exposure at the onset of flowering, another particularly sensitive lifestage. 

The results of this analysis (Table 2) indicate that there are no appreciable differences between 

the rates at which 25% inhibition (ICzs) occurs at each particular exposure life-stage and 

endpoint. It is important to note that 21-day biomass was not a measurement endpoint in these 

studies. In the guideline regulatory study for sulfometuron-methyl, pea biomass was an order of 

magnitude more sensitive than pea height. 

1 

2 

lb a.i./A 

However, the data do indicate that plants exposed to SU herbicides at the vegetative actively lifestage may also result in lower seed weight and smaller seeds than in the control, suggesting that 

sensitive plants exposed early in life may experience adverse impacts on fruit/seed numbers 

and/or fruit/seed weight. However, this issue is separate from the question of whether current 

guideline studies are protective of reproductive effects and needs to be explored more thoroughly 

by the PTT in the future. 
MRID 48915006 

MRlD 48915007 

MRID 48915008 

MRlD 48915009 

MRID 48915010 

MRID 48915011 

MRlD 48915012 

MRlD 48915001 

response to low rates of selected foliar- and soil- applied sulfonylurea and 

growth regulator herbicides. Weed Technology, 13: 753-758. 

Bhatti, M.A.; Al-.Khatib, K.; Felsot, A.S.; Parker, R. and S. Kadir. 1995. 

Effects of simulated chlorsulfuron drift on fruit yield and quality of sweet 

cherries (Prunus avium L.). Environmental Toxicology and Chemistry, 14 

(3): 537-544. 

Fletcher, J.S., T.G. Pfleeger, and H.C. Ratsch. 1993. Potential 

environmental risks associated with the new sulfonylurea herbicides. 

Environ. Sci. Technol. 27:2250-2252. 

Fletcher, J.S.; Pfleeger, T.G. and H.C. Ratsch. 1995. Chlorsulfuron 

influence on garden pea reproduction. Physiologia Plantarum, 94: 261-

267. 

Fletcher, J.S.; Pfleeger, T.G.; Ratsch, H.C.; and R. Hayes. 1996. Potential 

impact of low levels of chlorsulfuron and other herbicides on growth and 

yield of nontarget plants. Environmental Toxicology and Chemistry, 15 

(7): 1189-1196. 

Khan, M. and W.W. Donald. 1992. Sulfonylurea herbicides reduce 

survival and seed production of green and yellow foxtails (Setaria spp.). 

Weed Technology, 6: 284-290. 

Kjaer, C. 1994. Sublethal effects of chlorsulfuron on black bindweed 

(Polygonum convolvulus L.). Weed Research, 34: 453-459. 

Olszyk, D.; Pfleeger, T.; Lee, E.H.; and M. Plocher. 2009. Pea (Pisum 

sativum) seed production as an assay for reproductive effects due to 

herbicides. Environmental Toxicology and Chemistry, 28 (9): 1920-1929. 

Olszyk, D.; Pfleeger, T.; Lee, E.H.; and M. Plocher. 2010. Potato 

(Solanum tuberosum) greenhouse tuber production as an assay for asexual 

reproduction effects from herbicides. Environmental Toxicology and 

Chemistry, 29 (1): 111-121. 
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Weed Technology, 9: 468-476.