No enhancement in bioconcentration of organic contaminants by low levels of DOM

The aim of the present work was to systematically study the effect of low c oncentrations of dissolved organic matter (DOM) on the bioconcentration of organic contaminants, in order to show whether the phenomenon of enhanced b ioconcentration factors (BCFs), that has been reported in the literature, i s generally found at low levels of DOM or if BCF enhancements are more like ly due to a random scatter in the experimental data. The first part of the study tested the hypothesis that low levels of DOM affect the uptake kineti cs of organic contaminants, leading to transient enhancements of BCFs, rela tive to DOM-free controls, which could have been reported as BCF enhancemen ts in short-term studies. We found that the presence of low concentrations of two different types of DOM consistently decreased the bioconcentration o f benzo[a]pyrene (BaP) in the water flea Daphnia magna at all exposure time s (1-24 h), and that no transient BCF enhancements occurred. The second par t of the study systematically investigated if low concentrations of DOM fro m a wide range of different aquatic systems can cause enhancements in the b ioconcentration of organic contaminants. Water fleas were exposed to combin ations of four different organic contaminants (BaP, tetrachlorobiphenyl, pe ntachlorophenol and naphthalene) with low concentrations of 12 different ty pes of DOM that had been collected from various regions throughout Europe. In several of the DOM treatments, we found mean BCFs being higher than mean BCFs in the controls (especially for naphthalene). This shows that the exp erimental setup used in this study (and similarly in previous studies) can produce seeming BCF enhancements at low concentrations of DOM. However, sta tistical analyses showed that treatment means were not significantly differ ent from control means. Thus, this systematic study suggests that the BCF e nhancements that have been reported in the literature are more likely the r esult of random, experimental variations than the result of a systematic en hancement of bioconcentration. (C) 2001 Elsevier Science Ltd. All rights re served.