Bioavailability of atrazine, pyrene and benzo[a]pyrene in European river waters.

Thirteen river waters and one humic lake water were characterized. The effects of dissolved organic matter (DOM) on the bioavailability of atrazine, pyrene and benzo[a]pyrene (B[a]P) was evaluated. Binding of the chemicals by DOM was analyzed with the equilibrium dialysis technique. For each of the water samples, 24 h bioconcentration factors (BCFs) of the chemicals were measured in Daphnia magna. The relationship between DOM and other water characteristics (including conductivity, water hardness and pH), and bioavailability of the chemicals was studied by performing several statistical analyses, including multiple regression analyses, to determine how much of the variation of BCF values could be explained by the quantity and quality of DOM. The bioavailability of atrazine was not affected by DOM or any other water characteristics. Although equilibrium dialysis showed binding of pyrene to DOM, the bioavailability of pyrene was not significantly affected by DOM. The bioavailability of B[a]P was significantly affected by both the quality and quantity of DOM. Multiple regression analyses, using the quality (ABS270 and HbA%) and quantity of DOM as variables, explained up to 70% of the variation in BCF of B[a]P in the waters studied.

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 concentrations of dissolved organic matter (DOM) on the bioconcentration of organic contaminants, in order to show whether the phenomenon of enhanced bioconcentration factors (BCFs), that has been reported in the literature, is generally found at low levels of DOM or if BCF enhancements are more likely 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 kinetics of organic contaminants, leading to transient enhancements of BCFs, relative to DOM-free controls, which could have been reported as BCF enhancements in short-term studies. We found that the presence of low concentrations of two different types of DOM consistently decreased the bioconcentration of benzo[a]pyrene (BaP) in the water flea Daphnia magna at all exposure times (1-24 h), and that no transient BCF enhancements occurred. The second part of the study systematically investigated if low concentrations of DOM from a wide range of different aquatic systems can cause enhancements in the bioconcentration of organic contaminants. Water fleas were exposed to combinations of four different organic contaminants (BaP, tetrachlorobiphenyl, pentachlorophenol and naphthalene) with low concentrations of 12 different types 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 experimental setup used in this study (and similarly in previous studies) can produce seeming BCF enhancements at low concentrations of DOM. However, statistical analyses showed that treatment means were not significantly different from control means. Thus, this systematic study suggests that the BCF enhancements that have been reported in the literature are more likely the result of random, experimental variations than the result of a systematic enhancement of bioconcentration.

Toxicity of cadmium to Caenorhabditis elegans (Nematoda) in whole sediment and pore water--the ambiguous role of organic matter.

A bioassay using the nematode Caenorhabditis elegans was performed with natural sediment that had been spiked with organic matter (36-117 g total organic carbon/kg dry wt) and cadmium (Cd; 10-1,200 mg/kg wet wt). Whole sediment and pore water were tested to study the influence of particulate organic matter (POM) and dissolved organic matter (DOM) on Cd toxicity and to compare the toxicity of the two sediment phases. Toxicity was measured with nematode growth as test parameter. No toxicity was observed if sediment concentrations of Cd were below concentrations of acid-volatile sulfides (AVS). At higher Cd concentrations, toxicity in whole sediment and pore water increased with increasing organic content. This phenomenon was explained by an increase of DOM concentrations in organically enriched treatments and a resulting solubilization of Cd due to Cd complexation by DOM. Because DOM did not alter the bioavailability of Cd for the nematodes, bacteria, serving as food, might have functioned as vectors for Cd-DOM complexes, so that Cd could have become available in the gut of the nematodes. A higher toxicity in whole sediment compared to in pore water in the organically enriched treatments indicated that POM-bound Cd may have contributed to the toxicity of Cd to C. elegans.

In vivo laser-induced fluorescence detection of pyrene in nematodes and determination of pyrene binding constants for humic substances by fluorescence quenching and bioconcentration experiments.

The bioconcentration of pyrene by bacterivorous thread worms (nematodes) of the species Caenorhabditis elegans was studied with laser-induced fluorescence (LIF) spectroscopy, fluorescence imaging and a radiotracer method. The vibronic band intensities of the LIF spectra indicated that the microenvironment of pyrene in the nematodes was similar to a low-polarity solvent, and thus provided direct evidence that pyrene was accumulated in lipid-rich areas inside the nematodes. The concentration of pyrene in the nematodes was estimated from the monomer/excimer fluorescence intensity ratio. Results from this method were in fair agreement with results using 14C labeled pyrene for measuring pyrene bioconcentration. Preliminary results indicated that LIF measurements of pyrene may be possible even in single nematodes. Fluorescence microscopic observations revealed that pyrene was not adsorbed on the outside of the organisms, but was strongly concentrated in restricted areas inside the worms. In the second part of the study, the effects of six different humic substances (HS) on the bioconcentration of pyrene were investigated and sorption coefficients (KDOC) calculated from reductions in bioconcentration (KDOC(biol)) were compared with sorption coefficients measured with a fluorescence quenching technique (KDOC(flu)). The results of these two different experimental methods agreed well (with KDOC(biol) being slightly lower than KDOC(flu), indicating that the fraction of pyrene that was determined as freely dissolved by the fluorescence quenching method was comparable to the bioavailable fraction.

Effects of dissolved organic matter (DOM) on the bioconcentration of organic chemicals in aquatic organisms--a review.

Current knowledge on the effects of dissolved organic matter (DOM) on the bioconcentration of organic chemicals in aquatic animals (water fleas, mussels, amphipods and fish) is summarized. A graphical representation of the available data gives an overview of the magnitude of the observed effects. Most of the studies have shown decreases in bioconcentration in the presence of DOM (2 to 98% relative to DOM-free controls). However, at low DOM levels, up to 10 mg/L, also enhancements of bioconcentration due to DOM, ranging from 2 to 303% have been reported. Generally, the change in BCFW (Bioconcentration factor on a wet weight basis) per mg/L DOC was most pronounced at low levels of DOC. The data also show that DOM from different sources with different characteristics and quality can lead to substantial variations in the bioconcentration of organic compounds at comparable levels of DOC. While decreases in bioconcentration have generally been attributed to a lack of bioavailability of DOM-bound chemical, no mechanisms have been proposed to explain increased uptake of xenobiotics caused by DOM.