No abstract

Information on the aqueous solubilities of organic substances are important for understanding hydrophobic interactions in water and for assessing the distribution and toxicity of contaminants in aquatic environments. Environmental contaminants are frequently encountered as mixtures, and the behaviour of a compound in a mixture may not correspond to that predicted from the pure compounds data. In this study, solutions of ten binary aromatic mixtures were examined, each at several molar ratios. The five individual aromatics were benzene, 2-chlorotoluene, 2-sec-butylphenol, aniline, and 2-nitroanisole. The water solubilities of those individual compounds range from about 400 to about 40,000 mgj. For all these binary systems, the experimental results indicate that there are significant cosolute interactions on aqueous contaminant concentrations which appear dependent on the structures of the cosolutes. The UNIFAC model and an empirical QSAR (not given) model are used for the prediction and the correlation of the data, respectively. Both methods give reasonably good results.

Physico-chemical properties related to the bioavailability of xenobiotics in aquatic environments have been tested for their ability to identify chemicals with low bioconcentration potential. Cut-offs in lipophilicity (log K(OW) < 3 or > 10), solubility and volatility (log Henry constant <-11 [atm (mol L(-1))(-1)]), degradability (ready biodegradability, hydrolysis) and ionisation (>5% ionisation at pH 7) have been adopted and combined into a decision tree based on 382 industrial chemicals. The five-parameter classification scheme was externally validated with 49 pesticides and successfully confirmed with 83 bioaccumulative compounds. The applicability domain of the model has been described in terms of chemical classes (excluding polybrominated compounds (>4 Br), organometallics, compounds with perfluorinated fragments, substances with an acyclic alkyl moiety (chain length > C7) and thiols) and ranges of physico-chemical properties. The present tool allows to securely de-prioritize more than 50% chemicals of low concern with regard to the B criterion (BCF < 2000). Bioassays with compounds with these physico-chemical constraints may be waived because testing may be technically not possible and does not appear scientifically necessary in persistent, bioaccumulative, toxic (PBT) substances and risk assessments.