Differential acute toxicity of tetrachlorobenzene isomers to oligochaetes in soil and water: application of the critical body residue concept.

The acute, lethal potency of the 1,2,3,4-, 1,2,4,5- and 1,2,3,5-tetrachlorobenzene isomers was compared in the terrestrial and aquatic oligochaetes Eisenia andrei and Tubifex tubifex. 1,2,4,5-TeCB was neither lethal, nor produced any perceptible adverse effects, at lipid normalized concentrations predicted to be lethal according to the well-established critical body residue concept. If a narcotic is defined as a substance capable of inducing narcosis, rather than a substance displaying certain physical or chemical properties (e.g., log K(ow)), then we do not believe these findings challenge the critical body residue because by the former definition, 1,2,4,5-tetrachlorobenzene is not a narcotic.

Determining exposure dose in soil: the effect of modifying factors on chlorinated benzene toxicity to earthworms.

This study describes the comparison of multiple approaches for estimating the median lethal concentration of selected chlorinated benzenes (CBs) from an homologous series yielding acute toxicity to the earthworm Eisenia andrei in Webster soil. The coefficients of variation were significantly lower for solid-phase microextraction (SPME), tissue residue, and hexane-extractable based CB exposure estimates compared to nominal CB exposure estimates. The range of CB exposure estimates based on SPME, tissue residue, or nominal was narrower than lethal concentration exposure estimates based on hexane-extractable CBs. Despite the insignificant difference between the coefficients of variation for SPME and hexane-extractable based measures of CB exposure, the results of this study suggest that the use of SPME based estimates of exposure may improve the accuracy of ecological risk assessment when used an alternative to hexane-extractable (total soil CBs) due to a narrower range of medial lethal concentrations when comparing equipotent compounds.

Phenanthrene release from natural organic matter surrogates under simulated human gastrointestinal conditions.

The aliphatic region of natural organic matter (NOM) can retain polycyclic aromatic hydrocarbons (PAH) due to the presence of non-polar binding sites. Thus NOM may act as a vehicle for entry of PAH into the gastrointestinal system in man and animals. In this study, the release of phenanthrene from the aliphatic NOM surrogates cutin and cutan was measured under simulated human gastrointestinal formulations using three treatments designed to simulate the biological and chemical conditions of the gastrointestinal environment. The three experimental treatments were composed of fecal microorganisms, chyme, and chyme+fecal microorganisms. Water was used as a control treatment. Phenanthrene laden biopolymer and a C18 membrane were immersed in each treatment. Phenanthrene was extracted from each membrane and measured with HPLC. Membrane-associated phenanthrene was taken to represent the fraction that had desorbed from the biopolymer. Cutin was found to yield an average phenanthrene release 55% higher than cutan (94% vs. 39%). A significant decrease (p<0.05) in phenanthrene release was observed in both the chyme and chyme+fecal microorganism treatments as compared to the water treatment (control). The presence of enteric microorganisms did not significantly influence phenanthrene release and did not reduce phenanthrene bioaccessibility in gastrointestinal chyme. Over 80% of the phenanthrene in cutin was recovered in the C18 matrix and its relative amount was uninfluenced by the treatments. For cutan, only 25-50% of the phenanthrene was recovered, suggesting that cutin-associated phenanthrene was more loosely bound. These data demonstrate that the fractions of NOM retained phenanthrene to a varying extent and thus the predictions of phenanthrene bioavailability should also be assessed on the basis of the constituents of the NOM matrix.