Survey of levels of cadmium in oysters, mussels, clams and scallops from the Pacific Northwest coast of Canada

Abstract

Field and retail collections of bivalves from the Pacific Northwest, Canada, were analysed for cadmium concentrations by atomic absorption spectrophotometry (AAS). Both collections of varnish (Nuttallia obscurata) and manila (Venerupis philippinarum) clams contained cadmium concentrations of less than 0.5 µg g⁻¹, well below international safety guidelines of 1 and 2 µg g⁻¹ wet weight cadmium for the European and Hong Kong markets, respectively, as well as the 2 µg g⁻¹ safety guideline set by the Codex Alimentarius Commission (CAC). Cadmium concentrations in retail collections of the Pacific oyster, Crassostrea gigas, were generally above 2 µg g⁻¹ wet weight (range = 1.5–3.56 µg g⁻¹). Retail collections of the mussel, Mytilus spp., contained cadmium concentrations below the 2 µg g⁻¹ wet weight guideline, but not always the 1 µg g⁻¹ limit (range = 0.15−1.8 µg g⁻¹). However, field collections of Mytilus spp. contained cadmium concentrations between 0.35 and 4.00 µg g⁻¹ wet weight, and depending on sampling location, concentrations exceeded the CAC guidelines by more than two-fold. Locations where mussels had high cadmium concentrations correlated with regions that had previously reported high values for cadmium in Pacific oysters (r = 0.65; p < 0.05). Of the various shellfish analysed, the four species of scallops, Chlamys hastata, C. rubida, Crassadoma gigantea, and Patinopecten yessoensis, contained the greatest concentrations of cadmium, in excess of 5 µg g⁻¹ wet weight (range = 4.97–8.98 µg g⁻¹) with the greatest concentrations determined for C. gigantea. Cadmium concentrations in shellfish from the Pacific Northwest are greater than values reported for shellfish from other regions of the world and consumers need be aware of Health Canada consumption guidelines for shellfish from this region.

Keywords:

• exposure
• market basket survey
• metals – uptake
• metals analysis – atomic absorption spectrometry (AAS)
• heavy metals – cadmium
• seafood

Acknowledgements

Many people took part in this study, to whom the author is extremely grateful. The author wishes to acknowledge the technical excellence of Dave McKay, Tracey Brunjes, Jeff Christie, and Tyler Gray. Cadmium concentrations in scallops were part of a Co-Op study term for Denise Ding. Field collections were supplied by George Kruzynski and Bill Heath (mussels) and Jonathan Whiteley (clams). George Kruzynski also organized and oversaw the international laboratory calibration exercise without which none of the results would be worth reporting. Funding in part was through an NSERC discovery grant to LB (Grant Number 31-611307).