Determination of the dietary absorption efficiency of hexachlorobenzene with the channel catfish (Ictalurus punctatus)

Bioconcentration and endocrine disruption effects of diazepam in channel catfish, Ictalurus punctatus

Recently, the detection of pharmaceuticals in surface waters has increased worldwide. Pharmaceuticals are typically found in the environment at concentrations well below therapeutic levels in humans; however, their mechanisms of action may be largely unknown in non-target organisms, such as teleost species. Thus, chronic exposure to these types of compounds warrants further investigation. The goal of this study was to examine the potential for diazepam, a model benzodiazepine drug, to bioconcentrate in tissues of channel catfish and to examine its ability to interact with the endocrine system through modulation of steroid hormones and/or steroidogenic genes. To investigate the bioconcentration potential of diazepam, channel catfish (Ictalurus punctatus) were exposed to 1 ng/mL diazepam for seven days, followed by clean water for another seven days, using an abbreviated OECD 305 Fish Bioconcentration Test study design. This concentration of diazepam is well below environmentally relevant concentrations of diazepam (ng/L). To evaluate steroidogenic effects, fish were exposed to 1 ng/mL diazepam for seven days only. Steroid hormone concentrations were analyzed for various tissues, as well as expression of selected steroidogenic genes. Calculated bioconcentration factors for diazepam were well below regulatory threshold values in all tissues analyzed. No changes in steroid hormone concentration were detected in any tissue analyzed; however, the steroidogenic gene cytochrome P450 side chain cleavage (P450scc) was significantly down-regulated at day 5 and 3β-hydroxy steroid dehydrogenase (3β-HSD) was significantly down-regulated at day 7 in the gonad. These results indicate that although diazepam does not significantly bioconcentrate, low-level chronic exposure to diazepam may have the potential to interact with endocrine function by altering gene expression.

An evaluation of bioaccumulation data for hexachlorobenzene to derive water quality standards according to the EU-WFD methodology

Hexachlorobenzene (HCB) is a priority hazardous substance within the Water Framework Directive (WFD). For aquatic systems, the European Commission has derived quality standards (QS) for HCB in biota. However, in some countries a preference may exist for QS based on water concentrations. The conversion of biota QS into water QS can be done by dividing the quality standard for biota by a reliable bioaccumulation factor (BAF) or by the product of the bioconcentration factor (BCF) and the biomagnification factor (BMF) (BCF × BMF). An extensive literature review of HCB bioaccumulation was performed, and data on bioaccumulation, biomagnification and bioconcentration, both from the field and the laboratory, were assessed for their usefulness to recalculate biota standards into water standards. The evaluation resulted in 10 reliable values for field BAFs, with a geometric mean of 221 000 L/kg (5% lipid-normalized). Bioaccumulation factor measurements show a high variation of more than 1 order of magnitude. At lower trophic levels (algae, small zooplankton), accumulation of HCB already exceeds expected accumulation through equilibrium partitioning by far. This affects BAFs at higher trophic levels as well. Moreover, observed BAF values for HCB in fish cannot be easily explained from the age of the fish, but there is a significant increase with trophic level. Reliable values for laboratory BCFs for fish were retrieved from literature, partly with water-based exposure and partly with dietary exposure. The 5% lipid-normalized BCF of all these data is 12 800 L/kg. Regarding biomagnification, a number of reliable BMF and trophic magnification factor values, mostly determined in the field, were retrieved. From these data, an overall BMF of 3 per trophic level can be deduced. When comparing BCF values for fish multiplied by the BMF (12 800 × 3 = 38 400 L/kg) to the observed BAF values for fish (geometric mean 238 000 L/kg), there appears to be a large gap. Thus, the uncertainties surrounding values for bioaccumulation of HCB are high. Although the confidence in laboratory BCFs is higher, these data seem to be not relevant for small fish in the field. This makes it difficult to obtain a reliable BAF or BCF × BMF value to recalculate biota standards into water standards. On the other hand, biota concentrations in the field show a high variability that also hampers comparison with a fixed limit such as a quality standard. Thus, compliance checking using biota in the field means that a relatively large amount of fish will have to be used to obtain a reliable estimate. The following "tiered approach" is suggested: 1) calculate a water quality standard, using the BAF value that is most relevant for the trophic level to be protected, and 2) if this standard is exceeded in the field, sample representative biota in the field and compare concentrations of HCB in biota and water with their respective standards in a weight of evidence approach for compliance checking. In this way, unnecessary biota sampling can be avoided for reasons of efficiency and animal welfare.

Comparing laboratory and field measured bioaccumulation endpoints

An approach for comparing laboratory and field measures of bioaccumulation is presented to facilitate the interpretation of different sources of bioaccumulation data. Differences in numerical scales and units are eliminated by converting the data to dimensionless fugacity (or concentration-normalized) ratios. The approach expresses bioaccumulation metrics in terms of the equilibrium status of the chemical, with respect to a reference phase. When the fugacity ratios of the bioaccumulation metrics are plotted, the degree of variability within and across metrics is easily visualized for a given chemical because their numerical scales are the same for all endpoints. Fugacity ratios greater than 1 indicate an increase in chemical thermodynamic activity in organisms with respect to a reference phase (e.g., biomagnification). Fugacity ratios less than 1 indicate a decrease in chemical thermodynamic activity in organisms with respect to a reference phase (e.g., biodilution). This method provides a holistic, weight-of-evidence approach for assessing the biomagnification potential of individual chemicals because bioconcentration factors, bioaccumulation factors, biota-sediment accumulation factors, biomagnification factors, biota-suspended solids accumulation factors, and trophic magnification factors can be included in the evaluation. The approach is illustrated using a total 2393 measured data points from 171 reports, for 15 nonionic organic chemicals that were selected based on data availability, a range of physicochemical partitioning properties, and biotransformation rates. Laboratory and field fugacity ratios derived from the various bioaccumulation metrics were generally consistent in categorizing substances with respect to either an increased or decreased thermodynamic status in biota, i.e., biomagnification or biodilution, respectively. The proposed comparative bioaccumulation endpoint assessment method could therefore be considered for decision making in a chemicals management context.