Yves Couillard

Toxicity of sixty‐three metals and metalloids to Hyalella azteca at two levels of water hardness

The toxicity of all atomically stable metals in the periodic table, excluding Na, Mg, K, and Ca, was measured in one-week exposures using the freshwater amphipod Hyalella azteca in both Lake Ontario, Canada, and soft water (10% Lake Ontario). Metals were added as atomic absorption standards (63 metals), and also as anion salts for 10 metals. Lethal concentrations resulting in 50% mortality (LC50s) were obtained for 48 of the metals tested; the rest were not toxic at 1,000 microg/L. The most toxic metals on a molar basis were Cd, Ag, Pb, Hg, Cr (anion), and Tl, with nominal LC50s ranging from 5 to 58 nmol/L (1 to 58 nmol/L measured). These metals were followed by U, Co, Os, Se (anion), Pt, Lu, Cu, Ce, Zn, Pr, Ni, and Yb with nominal LC50s ranging from 225 to 1,500 nmol/L (88-1,300 nmol/L measured). Most metals were similarly or slightly more toxic in soft water, but Al, Cr, Ge, Pb, and U were >17-fold more toxic in soft water; Pd was less toxic in soft water. Atomic absorption (AA) standards of As and Se in acid had similar toxicity as anions, Sb was more toxic as the AA standard, and Cr and Mn were more toxic as anions. One-week LC50s for H. azteca correlate strongly with three-week LC50s and three-week effect concentrations resulting in 50% reduction in reproduction (EC50s) in Daphnia magna.

Steady-state distribution of metals among metallothionein and other cytosolic ligands and links to cytotoxicity in bivalves living along a polymetallic gradient

The present study was designed to assess the environmental effects of metals in a field setting. We explored exposure-->bioaccumulation-->effects relationships in freshwater molluscs exposed to metals in their natural habitat. Indigenous floater mussels (Pyganodon grandis) were collected from ten limnologically similar lakes located along a Cd, Cu and Zn gradient. Ambient free-metal ion concentrations were estimated as a measure of metal exposure. Metallothionein (MT) was measured in mussel gills and metal partitioning among the various cytosolic protein pools was determined by size exclusion chromatography. Various biomarkers were also measured, including malondialdehyde (MDA) concentrations in the gills and in the digestive gland, glutathione-peroxidase and glutathione-reductase activities in the digestive gland, and lipid concentrations in the gonad. Cadmium and MT concentrations in the gill cytosol increased along the contamination gradient, but Cu and Zn levels were independent of the ambient free-metal ion concentrations. The distribution of Cd among the various cytosolic complexes remained quite constant: 80% in the MT-like pool, 7% in the low molecular weight pool (LMW<1.8 kDa) and 13% in the high molecular weight pool (HMW>18 kDa). For these chronically exposed molluscs there was thus no threshold exposure concentration above which spillover of Cd occurred from the MT pool to other cytosolic ligands. However, the presence of Cd in the LMW and HMW fractions suggests that metal detoxification was imperfect, i.e. that P. grandis was subject to some Cd-related stress at low chronic exposure concentrations. Consistent with this suggestion, MDA concentrations, an indicator of oxidative stress, increased with gill cytosolic Cd. In the digestive gland, MDA concentrations were unrelated to any of the measured metals, but glutathione-peroxidase and glutathione-reductase activities increased with gill cytosolic copper. We speculate that cytosolic Cu catalyses the production of reactive oxygen species, to which the organism reacts by increasing activities of the two enzymes, thus preventing the accumulation of reactive oxygen species. Lipid concentrations in the gonad did not decrease with any of the measured toxicological parameters, suggesting that energy reserves for reproduction were not compromised in the metal-contaminated mussels. The results of the present study, where chronically exposed bivalves were collected from their natural habitat along a metal contamination gradient, contrast markedly with what would have been predicted on the basis of experimental metal exposures, and clearly demonstrate the need to study metal exposure-->bioaccumulation-->effects relationships in natural populations.

A test of the integrity of metal records in sediment cores based on the documented history of metal contamination in Lac Dufault (Québec, Canada)

There is an important volume of published information on Lac Dufault (Québec) which describes the history of metal inputs over 70 years and the changes that occurred in the lake as a result of this contamination. We used this abundant source of chronological markers to test the hypothesis that lake sediments can provide true historical records of trace metal loading from metal mining. Sediment cores were obtained from the deepest zone of the lake (19 m). The sediments were dated using 210Pb and 137Cs and they were analyzed for total elemental concentrations (Ca, Cd, Cu, Fe, P, Pb, S, Zn). Metal profiles in the sediment core preserved the distinct signatures of different mine exploitations documented in the lake watershed. In particular, the core recorded: the beginning of industrialization in 1926; increasing sedimentation rates associated with perturbations in the lake watershed; the maximum of sediment [Cu] and the contemporary exploitation of ore bodies rich in Cu; the maximum of sediment [Fe] and the contemporary production of pyrite by a mining operation; the low sediment [Cu] and [Zn] in the 1950s and the low contemporary production of these metals by mining operations; the maximum of sediment [Cd] and the contemporary production of Cd by a subsequent mining operation. Anomalies in the distribution of 214Pb activities in sediments reflected the intensity of acid mine drainage (AMD). There is good evidence that the lake resisted acidification from this AMD for the last thirty years. Overall, our results support the thesis that profiles of sedimentary Cd, Cu, Zn, Pb and Fe levels reflect the past history of metal input to Lac Dufault.

Molecular size cutoff criteria for screening bioaccumulation potential: Fact or fiction?

It has been asserted that, when screening chemicals for bioaccumulation potential, molecular size cutoff criteria (or indicators) can be applied above which no, or limited, bioaccumulation is expected. The suggested molecular size values have increased over time as more measurements have become available. Most of the proposed criteria have been derived from unevaluated fish bioconcentration factor (BCF) data, and less than 5% of existing organic substances have measured BCFs.We critically review the proposed criteria, first by considering other factors that may also contribute to reduced bioaccumulation for larger molecules, namely, reduced bioavailability in the water column, reduced rate of uptake corresponding to reduced diffusion rates, and the effects of biotransformation and growth dilution. An evaluated BCF and bioaccumulation factor (BAF) database for more than 700 substances and dietary uptake efficiency data are compared against proposed cutoff values. We examine errors associated with interpreting BCF data, particularly for developing molecular size criteria of bioaccumulation potential. Reduced bioaccumulation that is often associated with larger molecular size can be explained by factors other than molecular size, and there is evidence of absorption of molecules exceeding the proposed cutoff criteria. The available data do not support strict cutoff criteria, indicating that the proposed values are incorrect. Rather than assessing bioaccumulation using specific chemical properties in isolation, holistic methods that account for competing rates of uptake and elimination in an organism are recommended. An integrated testing strategy is suggested to improve knowledge of the absorption and bioaccumulation of large substances.

The amphipod Hyalella azteca as a biomonitor in field deployment studies for metal mining.

Specimens of the amphipod Hyalella azteca were deployed, in June-July 2003, along metal contamination gradients in two rivers affected by metal mining in the Abitibi-James Bay region, northwestern Québec. The amphipods were placed along with natural food items in small, acrylic cages and left in six riverine sites for 17 days. Twelve metals (As, Cu, La, Mn, Ni, Sb, Se, Tl, U, V, Zn, and CrO4(2-) modelled by WHAM VI) in transplanted H. azteca varied along metal contamination gradients in a consistent manner, i.e., as a function of metal exposure. Bioaccumulation of As, Cr, La, Ni, Sb, Se, Tl, U and V, as defined by a field BCF, was significantly correlated with their chronic toxicity potential towards the amphipod. We conclude that H. azteca may be a useful field biomonitor for metal mining. In addition, our results suggest that such biomonitoring programs should include less studied elements such as Se in mining effluents.

Towards Consistent Evaluation of the Persistence of Organic, Inorganic and Metallic Substances

Several criteria, including persistence (P), bioaccumulation (B), its related factor bioavailability, toxicity (T), and potential for long range transport (LRT) are currently applied when assessing the environmental hazard and risk associated with the use of chemicals of commerce. Whereas information on B and T criteria may be obtained by experimental measurement using standard tests or by the use of mass balance models, in the case of P and LRT no such standard tests exist, except for certain degradation rates in single media. Nor can these properties be measured in the environment at large. Here we focus on the criterion of persistence and its evaluation using steady-state multimedia mass balance models. It is concluded that it is possible to assess the persistence of all chemical substances including organics, inorganics, and metals using a common methodology in which mass balance models are applied to describe the substances behavior in a specified environment or “unit world.” This avoids inconsistent evaluation and excessive regulatory fragmentation, which is likely if assessment procedures are specific to classes of chemicals. It is essential that persistence be recognized as only one of several factors influencing hazard and risk. Regulatory actions must also thus reflect other attributes such as toxicity, bioaccumulation, quantities used, and the societal value of the substances.