Exposure regression analyses

Somewhat different approaches were used in analysing and reporting the neurobehavioural results from the other prospective studies. Instead of grouping subjects into different levels of exposure, regression analyses were applied to data across the entire range of PbB levels. This approach does not identify a threshold at which effects occur, but it does provide a useful estimate of the quantitative relationship between PbB levels and changes (in this case, decrements) in Bayley MDI scores. Recent results from the Cincinnati study indicate, for example, that 6-month-old male infants show an 8-point decrease in the MDI for every 10-jUg/dl increase in PbB level (Dietrich et al,... 

According to the investigators, the lack of association with lead rank indicated that the effect of lead was due to current rather than past lead exposure. The probability that a child was hyperactive increased significantly with increasing PbB levels (as PbB percentile rank within age group). The probability of speech impairment, however, was not related to blood lead levels. Linear regression analysis... 

The team led by Whyatt used regression analysis to assess whether there was a difference in the association between chlorpyrifos exposure and birth outcome before and after the EPA s action in the summer of 2000 which had ended residential use of chlorpyrifos. Prior to 2001, chlorpyrifos clearly had an impact on birth outcome, but after the EPA action taken in June 2000, levels of exposure declined and there was no longer a statistically significant association between insecticide exposure and birth outcome (Whyatt et al., 2004, 2005). This study provides encouraging evidence linking an action driven by the FQPA to a significant reduction in prenatal and infant exposures and risk. 

Two data sets of LC50 values for different time periods of exposure were analyzed using a linear regression analysis of the log-log transformation of a plot of C vs t to derive values of n for monomethylhydrazine. 

Rat and mouse lethality data from the well-conducted study of Zwart et al. (1990) also suggest that Haber s law is valid for phosgene. The study by ten Berge et al. (1986) has shown that the concentration-exposure-time relationship for many irritant and systemically acting vapors and gasses can be described by the relationship Cnxt=k. When the 10- to 60-min rat LC50 data are utilized in a linear regression analysis a value of the exponent, n, of 0.93 is obtained. The mouse 10- to 60-min lethality data yield a value of 1.3 for n. 

When data are lacking for desired exposure times, scaling across time may be based on the relationship between concentration and exposure duration (Cn xt=k) when a common end point is used (ten Berge et al. 1986). The end points for HCN are incapacitation and lethality. Regression analysis of the data of Sakurai (1989), using incapacitation concentrations for mice for the exposure durations of 5, 10, 20, and 30 min, results in a value for n of 1.6. Regression analysis of the incapacitation data of Purser et al. (1984) for monkeys for the time period of 8 to 19 min results in a value for n of 2.1 (Appendix A, Figure A-l). These studies were of relatively short duration. 

Blair et al. (1998) performed a retrospective cohort mortality study of 14 457 workers employed for at least one year between 1952 and 1956 at an aircraft maintenance facility in the United States. Among this cohort were 6737 workers who had been exposed to carbon tetrachloride (Stewart et al., 1991). The methods used for this study are described in greater detail in the monograph on dichloromethane. An extensive exposure assessment was performed to classify exposure to trichloroethylene quantitatively and to classify exposure (ever/never) to other chemicals qualitatively (Stewart et al., 1991). Risks from chemicals other than trichloroethylene w ere examined in a Poisson regression analysis of cancer incidence data. Among women, exposure to carbon tetrachloride was associated with an increased risk of non-Hodgkin lymphoma (relative risk (RR), 3.3 95% CI,... 

The relationships between Daphnia magna mortality and the concentrations of the components in the exposure solutions were explored by regression analysis. 

Using regression analysis based on Cox s proportional hazards model, Ott and Zober (1996) found evidence of association between 2,3,7,8-TCDD exposure and digestive cancer (conditional risk ratio of 1.46 95% 0=1.13-1.89) the primary tumor sites were the liver, stomach, and pancreas. 

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