Drastic difference in cadmium concentration in mussels (Mytilus chilensis) observed between seasons in natural bed and aquaculture systems in Chile

Globally, Chile is the second largest producer of mussels, with 99% of production concentrated in the inland sea of the Los Lagos Region, Southern Chile. This study reveals that seasons produce a drastic difference in the cadmium concentration (Cd) in marine mussels in bay, channel, and fjord ecosystems in this area. As the global mussel industry continues its rapid expansion, a complete understanding of cadmium pathways is critical in order to minimize the cadmium content in harvests. In this study, biweekly sampling was conducted in Chiloé (Southern Chile), during five consecutive seasons from June 2014 to November 2015. Cadmium in the soft tissues (ST) and in the content of the digestive gland (CDG) of Mytilus chilensis were investigated, in addition to resuspensions and seston to determine the effect of the seasons on metal bioassimilation capacity. In spring, the (Cd) between CDG and ST varied by approximately 2 mg Cd kg⁻¹ dry mass (DM). In summer and autumn, the (Cd) in CDG increased from 3 to 6 mg Cd kg⁻¹ while the (Cd) in ST decreased from 2.5 to 1.5 mg Cd kg⁻¹ DM. The three ecosystems showed the same cadmium bioconcentration trends in all seasons, revealing coherent global trends. These findings should caution the industry and coastal populations about the seasonal variability and intensity of cadmium metal transfer to biofilters, especially because of the adverse effects of cadmium consumption on human health. Additionally, this study found that mussels in natural beds concentrate more Cd (> 1 mg Cd kg⁻¹ DM) than in industrial facilities. Multiregression analysis showed and explained the cadmium in CDG for three ecosystems: channel (R² 0.9537), bay (R² 0.5962), and fjord (R² 0.4009). The independent variable nocturnal seston was able to explain the increase in cadmium.