Relative genotoxic activities of pesticides evaluated by a modified SOS microplate assay.

The genotoxic activities of 47 pesticides were determined using a modified SOS microplate assay in which the induction of beta-galactosidase in E. coli PQ37 was used as a quantitative measure of genotoxic activity. The results were compared with those obtained with anethole, curcumin, and capsaicin, a few examples of naturally occurring compounds present in foods. The assays were conducted with pesticides dissolved either in a suitable solvent, such as 10% DMSO in physiological saline or dispersed in sodium taurocholate micelles, to simulate conditions in the small intestine from where these substances are normally absorbed from the diet. 4-Nitroquinoline oxide (4-NQO) served as the reference standard of a direct acting mutagen. In micellar form, 4-NQO and 25 of the 47 pesticides tested showed significantly higher genotoxic activities than when they were tested in an organic solvent. In micellar form the SOS inducing potency of 4-NQO was almost twice as high as in 10% DMSO in physiological saline. In taurocholate micelles, the five most active compounds had activities in the range of 1,234-3,765 units/mumol and in the order of decreasing activities they were ranked as follows: malathion > dichlorvos > lindane > chlordane > endrin. They were significantly less active than 4-NQO (less than 40%). In micellar solution the naturally occurring compounds, anethole, curcumin, and capsaicin gave activities of 4,594, 928, and 809 units/mumol, respectively. These studies show that genotoxicity may depend upon the environment in which cells are exposed to these potential genotoxins. It appears that testing of the more hydrophobic compounds, both synthetic and naturally occurring, are needed.

Quantitative assessment of groundwater quality using a biological indicator: some preliminary observations.

The genotoxicity of groundwater was evaluated, using a novel application of the SOS microplate assay (SOSMA). Organic residues were extracted from groundwater samples from Maryland, Pennsylvania, and Delaware by using C-18 bonded silica solid phase extraction tubes. Total organic carbon content (TOC) of water samples was also determined. The genotoxicity of the extracts was determined by the SOSMA. Relative activity (RA) as determined by the SOSMA is a quantitative measure of genotoxicity based on a comparison to the activity of the mutagen, 4-nitroquinoline oxide. Low levels of RA (about 2x background) were detected in waters from sites within these states. There was considerable temporal and spatial variation in the observed RA, but no definite patterns were observed in the variation. Between sampling sites there was a positive correlation between RA and TOC; however, this relationship appeared to be reversed occasionally within a sampling site. The extraction and bioassay methods provide an easy and relatively inexpensive means of determining water quality.