Page 1 of 5 UNITED STATES ENVIRONMENTA L PROTECTION A GENCY

WASHINGTON, D.C. 20460 OFFICE OF PREVENTION, PESTICIDE S AND TOXIC SUBSTANCES MEMORANDUM Date : March 15, 2011 SUBJECT: Bromox yn il. Benchmark Dose Analy sis on Supernumerary Ribs in Three Developmental Toxicity

Studies PC Code: 035301, 035302 DP Barcode: D374609 Decision No.: 425581 Registration No. : 264 - 1023 Petition No.: 9F76 78 Regulatory Action: Section 3 Registration Risk Assessment Type : Single Chemical/ Aggregate Case No.: 2070 T XR No.: 0055648 CAS No.: 1689 - 84 - 5, 1689 - 99 - 2 MRID No.: 00116558 , 40466802 40 CFR: 180.324 FROM: My

ron S. Ottley , Ph .D., Senior Bi ologist Risk Assessment Branch III (RAB3) Health Effects Division (HED) (7509P) THROUGH: Paula Deschamp, Branch Chief

Risk Assessment Branch III (RAB3) Health Effects Division (HED) (7509P) TO: Bethany Benbow, RM#23

Registratio n Division (7505P) I . BACKGROUND In the previous risk assessment (D246944.mem, B. Madden 6/24/1998) , dose - response data on supernumerary

ribs from three studies were considered together in hazard characterization and hazard identification. Specifically , a NOAEL of 4 mg/kg/day from Rubin and Ny ska (1982) was combined with a LOAELof 5 mg/kg/day from Baker & Cropping (1981). Based on this combined evaluation, the previous assessment described concern over the steepness of the dose response curve and as a result the FQPA 10X Safety Factor was retained. In the last few ye ars, HED has increased its use of benchmark dose (BMD) anal ys is in risk assessment. In an effort to better characterize the dose response relationship for supernumerary ribs in rat fe tuses, a B MDPage 2 of 5

anal ys is was conducted on Studies A, B and C at EPA’s National Center for Environmental Assessment by

statistician Jeff Gift, Ph.D. , using the fetal and/or litter data available from each study report using EPA’s Benchmark Dose Software (BMDS, Version 2.). NCEA provided the full analy sis for each study (including the BMD outputs and plots). Only the plots for the best BMDS run for each study presented in this memo. However, the complete results of all anal ys es are presented as attachments to this memo . Briefl y, because of the nature of the data available from each study, different BMD anal ys es were conducted for each. These are relatively old studies and the individual pup data were not available for 2 of 3 studies. In the case of develop mental studies, i t is ty pical for the responses of pups in the same litter to be more similar to each other than to the responses of pups in different litters (“intra - litter correlation”, or “litter - effect”). When conducting BMD anal ys es of developmental studies, n ested models are the preferred approach since these models incorporate two parameters to address this issue : litter - specific covariate (L SC) and intra - litter correlation (IL C). The highest confidence anal ys is is for the Rubin & Nyska study (study A) where individual fetus data were available and a nested analy sis was completed. The lack of individual animal data for the other two studies (B & C) impacts the degree of confidence on the BMD anal ys is. HED can, however, use the BMD analy sis of al l three studies to provide an improved evaluation of the dose response curve compared with that performed in the previous risk assessment, and thus inform the magnitude of the FQPA SF. I I . SUMMARY of RESULTS Study Analysis BMD mg/kg/day BMDL mg/kg/day Co mment Study A (Rubin & Nyska 1982 ) nested dicho to mous data

analysis, using individual litter and fetus data 13.66 8.34 Availability of individual data from

both litters and fetuses allows integration of both into the same analysis Study B (Baker & Crop ping 1981 ) dichotomous data analysis, using

the litter as the subject and # litters with anomalies as the response 1.06 0.75 Lack of individual litter and fetus

data disallows any accounting for litter variation or inter- litter correlation ; this is the lowest confidence BMD run Study C (Rogers et al. 1991 ) continuous data analysis, using

mean percent/litter 9.80 8.86 Lack of individual litter and fetus

data disallows any accounting for litter variation or inter- litter correlation . Analysis is based on mean data only. 1. Study A: Rubin & Ny ska (1982) The current DER states that the NOAEL and LOAELfor this study are 4 mg/kg/day

and 12.5 mg/kg/day , respectively . The data - set for this study included both individual litterPage 3 of 5 and individual fetus data, whi ch allows for the “nested dichotomous” anal ysis. This anal ys is produced high confidence results. The benchmark response of 5% ‘extra risk’ (i.e., incidence above the background) was used here. The use of a BMR5 is normally used for developmental endpoint s. It is notable that the BMD5 and BMDL5 are both higher than the NOAEL of 4 mg/kg/day .

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

0 5 10 15 20 25 30 35 40Fraction Affected

dose Nested Logistic Model with 0.95 Confidence Level

14:44 12/02 2010 BMDL BMD Nested Logistic

2. Study B: Baker and Cropping (1981) T here is low confidence in the results of the Study B anal ys is because the data needed for meaningful and reliable analy sis , s uch as individual animal and litter variation, w ere not available from the study , rendering the data less reliable. However, visual inspection of the graph shows large variability of the data, suggesting that there is no meaningful difference between the control group and the low dose level (5 mg/kg/day).Page 4 of 5 0 0.2 0.4 0.6 0.8 1

0 5 10 15 20 25 30 35Fraction Affected

dose Quantal Linear Model with 0.95 Confidence Level

13:50 12/02 2010

BMDL BMD Quantal Linear

3. Study C: Rogers et al (1991) Similar to Baker and Cropping (1981), the individual pup data are not available, thus limiting the utility

of the BMD values. However, visual inspection of the plots s hows a shallow dose - response relationship at the low and mid dose such that the effects at the mid dose are not meaningfull y different from the control or low dose.

0 10 20 30 40 50 60 70 80

0 2 4 6 8 10 12 14Mean Response

dose Exponential Model 2 with 0.95 Confidence Level

14:47 12/02 2010 BMD BMDL ExponentialPage 5 of 5

I II . DISCUSSION The previous risk assessment used study A and study

B as co - critical studies and established the NOAEL of 4 mg/kg/day

based on study

A, and the LOAEL of 5 mg/kg/day based on Study

B. These values suggest a very steep dose - response curve, which provided the basis for the retaining of the 10X FQPA factor. Since that time, use of BMD anal ys es in HED assessment has accelerated, and the RAB3 Risk Assessment Team considered this as a good opportunity to use a more refined dose - response approach. BMD modeling uses the entire dose - response curve, considers the variability of the entire data - set, and takes sample size into account instead of just looking at a single point (NOAEL or LOAEL) for establishing a point of departure. Thus, BMD modeling provides an objective re - consideration of the available dose - response data. Study A provided the individual fetal and litter data needed to assess changes in incidence/litter of supernumerary

ribs with dose level, allowing a nested approach to analysis which integrates litter and fetal data. For the two studies without individual animal data (B and C), visual inspection of the graphs suggest that the dose - response curves are more shallow than previously interpreted. As such, this anal ys is reduces, if not alleviates, the previous concern over the steepness of the dose - response curve relate d to the supernumerary ribs and retention of the FQPA 10X. At this time, the RAB3 Team has concluded that HED can have confidence in the NOAEL of 4 mg/kg/day and use it as the point of departure for supernumerary ribs, without the need to retain a 10X FQP A factor. It is important to note that this analy sis is limited to a single endpoint and was conducted for the purpose of evaluating the dose - response data onl y from the supernumerary ribs and thus may

not appropriate for use in setting other points of departure. Specifically , the BMDL 5 of 8.34 mg/kg/day it is not protective of the decreased body weight gain observed at 5 mg/kg/day in F1 and F2 parents in a multi - generational reproduction study , or the decreased body weight gain, panting and liquid fec es in female dogs at 5 mg/kg/day in a 90 - day

oral toxicity

study . IV. ATTACHMENTS 1. Jeff Gift cover email 2. BandC 1981 -- BMD analy sis of Baker & Cropping (1981) study data 3. Rand1982 - BMR05

– BMD anal ys is of Rubin & Naska (1982) study data 4. Rand1982 - BMR10

– BMD anal ys is of Rubin & Naska (1982) study data 5. Rogers1981 - 1Std

– BMD anal ys is of Rogers, Francis et al. (1991) study data 6. Data set MRID 00116558 B aker & C ropping 1981 7. Data set MRID 40466802 R ubin & N ys ka 1982 8. Data set Rogers Francis et al 1981