Mutagenicity of chloroaniline/lignin metabolites in the Salmonella/microsome assay

Chloroanilines are constituents of many agrochemicals and have been found to be metabolized to succinic acid conjugates, e.g., succinamides and succinimides. The mutagenic potential of five chloroanilines and their succinamides and succinimide derivatives have been tested with two strains of Salmonella typhimurium (TA98 and TA100) with and without rat hepatic microsomal fraction. None of the compounds produced a dose response effect with a two-fold increase in revertants indicating that these compounds are not mutagens or promutagens in these assays.     

Residues and mutagenicity of captan applied to apple trees and potential human exposure

The fungicide captan (cis-N-((trichloromethyl)thio) 4-cyclo-hexene-1,2-dicarboximide) was applied at the rate of 2.4 g/l to apple trees (c.v. Golden Delicious) individually or as part of a standard treatment program where it was applied eight times during the growing season together with several pesticides. Leaf samples (100 discs of 2.2 cm diameter) were collected from treated and control trees before treatment and at 0, 1, 3, 7, 14, 28, 56, 90 and 112 days after treatment. Fruit samples were taken at mid-season (56 days) and at harvest (112 days). The objective of this study was to determine the captan residue and mutagenicity of leaf and fruit extracts to ascertain the potential health hazard to agricultural workers in these orchards. Surface residues were extracted from leaves and fruits with methylene chloride. These extracts were subsequently analyzed for captan by gas-liquid chromatography (GLC) utilizing an electron-capture detector, and for mutagenicity with two strains (TA98 and TA100) of Salmonella typhimurium, with and without microsomal enzyme activation. Positive mutagenic effects were observed with strain TA100 at 0-14 days post spray, even with extracts from one leaf disc's surface (3.8 cm2) of the single treatment. Captan residues in these samples indicated a decline from 9.3 micrograms/cm2 at 0 days to 0.80 micrograms/cm2 at 14 days and a trace after 112 days. With the standard treatment, in which captan was incorporated eight times in the program starting at the 7-day interval, leaf extracts showed mutagenic activity at 7, 14, 28 and 90 days. Captan residues at these intervals were 11.4, 5.0, 4.1 and 3.4 micrograms/cm2, respectively. Fruit sample extracts of the standard spray were mutagenic to the tester strains TA100 and TA98 both at mid-season and at harvest. Residues of captan on fruits declined from 10.4 micrograms/cm2 at mid-season to 1.1 micrograms/cm2 at harvest. No mutagenic activity was detected with extracts from fruit samples from the single captan application.     

The effect of metal catalysts on the formation of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran precursors

The catalytic effects of copper and iron compounds were examined for their behavior in promoting formation of chlorine (Cl₂), the major chlorinating agent of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), in an environment simulating that of municipal waste fly ash. Formation of Cl₂ occurred as a result of a metal-catalyzed reaction of HCl with O₂. Catalytic activity was greatest at a temperature of approximately 400 °C, supporting a theory of de novo synthesis of PCDDs and PCDFs on fly ash particles downstream of waste combustion.     

Comparing computing formulas for estimating concentration ratios

The purpose of this paper is to provide guidance on the choice of computing formulas (estimators) for estimating average concentration ratios and other ratio-type measures of radionuclides and other environmental contaminant transfers between ecosystem components. Mathematical expressions for the expected value of three commonly used estimators (arithmetic mean of ratios, geometric mean of ratios, and the ratio of means) are obtained when the multivariate lognormal distribution is assumed. These expressions are used to explain why these estimators will not in general give the same estimate of the average concentration ratio. They illustrate that the magnitude of the discrepancies depends on the magnitude of measurement biases, and on the variance and correlations associated with spatial heterogeneity and measurement errors. This paper also reports on a computer simulation study that compares the accuracy of eight computing formulas for estimating a ratio relationship that is constant over time and/or space. Statistical models appropriate for both controlled spiking experiments and observational field studies for either normal or lognormal distributions are considered. Our results indicate that for either type of study the geometric mean is generally preferred if the lognormal distribution applies. However, the geometric mean has the disadvantage that its expected value depends on n, the number of measurements taken. Ricker's estimator, $\text{R}\text{?}{}_{\mathrm{rt}}$, appears to perform worse than the other estimators studied when the observations are lognormal. All eight estimators appear to be equally accurate for the controlled spiking study when data are normally distributed. For observational field studies when data are normally distributed the ratio of means or slight modifications thereof are preferred to other estimators investigated. Before one chooses a computing formula for estimating a concentration ratio, thought should be given to what target value needs to be estimated to satisfy study objectives, and to whether the normal or lognormal distribution is a more realistic model. The geometric mean performs well for lognormal distributions, but comparison of geometric means or of a geometric mean with environmental limits can be misleading if n is small. The arithmetic mean of ratios is a conservative choice in that it will always give a larger estimate than will the geometric mean. It may also be severely biased when data are lognormal and the variances of measurement errors are large. The ratio of the means is a reasonable choice if the distribution is normal. The median of the observed ratios, $\text{R}\text{?}{}_{\mathrm{<mtext>md</mtext>}}$, is useful estimate since it is easily obtained and has an easily understood interpretation as the point above which and below which 50% of the observed ratios lie. Also, it is appropriate no matter what the distribution of the observed ratios may be. Confidence limits on the median are also easily obtained. Finally, while this paper emphasizes applications in radionuclide research, our results should be applicable to a wide range of environmental contaminants since many contaminants have approximately lognormal distributions.