Inverse relationship between bioconcentration factor and exposure concentration for metals: Implications for hazard assessment of metals in the aquatic environment

Abstract

The bioconcentration factor (BCF) and bioaccumulation factor (BAF) are used as the criteria for bioaccumulation in the context of identifying and classifying substances that are hazardous to the aquatic environment. The BCF/BAF criteria, while developed as surrogates for chronic toxicity and/or biomagnification of anthropogenic organic substances, are applied to all substances including metals. This work examines the theoretical and experimental basis for the use of BCF/BAF in the hazard assessment of Zn, Cd, Cu, Pb, Ni, and Ag. As well, BCF/BAFs for Hg (methyl and inorganic forms) and hexachlorobenzene (HCB) were evaluated. The BCF/BAF data for Zn, Cd, Cu, Pb, Ni, and Ag were characterized by extreme variability in mean BCF/BAF values and a clear inverse relationship between BCF/BAF and aqueous exposure. The high variability persisted when even when data were limited to an exposure range where chronic toxicity would be expected. Mean BCF/BAF values for Hg were also variable, but the inverse relationship was equivocal, in contrast with HCB, which conformed to the BCF model. This study illustrates that the BCF/BAF criteria, as currently applied, are inappropriate for the hazard identification and classification of metals. Furthermore, using BCF and BAF data leads to conclusions that are inconsistent with the toxicological data, as values are highest (indicating hazard) at low exposure concentrations and are lowest (indicating no hazard) at high exposure concentrations, where impacts are likely. Bioconcentration and bioaccumulation factors do not distinguish between essential mineral nutrient, normal background metal bioaccumulation, the adaptive capabilities of animals to vary uptake and elimination within the spectrum of exposure regimes, nor the specific ability to sequester, detoxify, and store internalized metal from metal uptake that results in adverse effect. An alternative to BCF, the accumulation factor (ACF), for metals was assessed and, while providing an improvement, it did not provide a complete solution. A bioaccumulation criterion for the hazard identification of metals is required, and work directed at linking chronic toxicity and bioaccumulation may provide some solutions.

Can Nassarius reticulatus be used as a bioindicator for Hg contamination? Results from a longitudinal study of the Portuguese coastline

“…The negative correlation feature seems to be a general trend for mercury, and it has been previously reported for other molluscs (McGeer et al, 2003) and fish (Parks et al, 1989). Through bioaccumulation and biomagnification processes (mainly of organic forms of mercury) throughout food webs involving molluscs and economically important fish species may retain an excessive mercury load in regions with a low Hg load and highly exploited coastal areas, representing therefore an unexpected risk to human health.…”

“…For instance, the presence of sulfides in the sediments may strongly bound the Hg [II] and make it unavailable to the biota (Beckvar et al, 1996). On the other hand, McGeer et al (2003) made an extensive literature review regarding the relationship between bioconcentration/bioaccumulation factors and the exposure concentration for metals in aquatic organisms. They reported an accumulation of mercury in molluscs which contrasts with that observed in other phyla, specifically fish and arthropods, since molluscs show a reduction, instead of an increase, in the tissue concentration of Hg as inorganic Hg exposure increases.…”

Trophic Transfer of Trace Elements in an Isotopically Constructed Food Chain From a Semi-enclosed Marine Coastal Area (Stagnone di Marsala, Sicily, Mediterranean)

“…However, metal uptake and adsorption through gills and body surfaces are important exposure pathways for aquatic organisms (Sayeed et al 2000;Ahlf et al 2009). In addition, trace metals are generally actively regulated and subject to binding-site competition (McGeer et al 2003). Furthermore, several physical and biological factors, including geography, sex, age, and body condition, affect metal deposition in animal tissues (Dehn et al 2006).…”

Toxicological availability of nickel to the benthic oligochaete Lumbriculus variegatus

“…An increase in bioaccumulation may be a sign of active metal uptake and not toxicity in the case of metal deficiency (Muyssen and Janssen, 2002;Bossuyt and Janssen, 2003). Thus, bioaccumulated metals may not always reflect toxic effects (McGeer et al, 2003).To our knowledge, the applicability of the SEM-AVS concept to predict the absence of chronic, sub-lethal toxicity of nickel to a benthic organism exposed in single-species laboratory toxicity tests has not been demonstrated. In this study, the hypothesis tested is that Ni 2+ in the pore water determines chronic toxicity to L. variegatus.…”