Seasonal levels of heavy metals in soft tissue and muscle of the pen shell Atrina maura (sowerby, 1835) (bivalvia: Pinnidae) from a farm in the southeastern coast of the gulf of California, Mexico

The pen shell (Atrina maura) is a filter-feeder bivalve that may accumulate metals in its body. The objective of this study was to determine seasonal concentrations of copper (Cu), chromium (Cr), cadmium (Cd), nickel (Ni), lead (Pb), arsenic (As), zinc (Zn), and mercury (Hg) in soft tissue and muscle of A. maura cultivated in a farm located in the southeastern coast of the Gulf of California from summer 2011 to summer 2012. Except for Cu, the higher metal concentrations were found during the dry season (winter 2011-spring 2012). The mean values in soft tissue fluctuated from 0.064 ± 0.01 µg/g (dry weight [dw]) for Hg to 485.66 ± 71.12 µg/g (dw) for Zn, while for muscle they varied from 0.058 ± 0.03 µg/g (dw) for Hg to 64.83 ± 4.90 µg/g (dw) for Zn. Concentrations of cadmium (18.15 µg/g in soft tissue and 1.82 µg/g in muscle, wet weight [ww]) and lead (2.31 µg/g in soft tissue, ww) exceeded the permissible limits (36.3, 3.64, and 2.31 times, respectively) recommended by the sanitary regulations of the official mexican standards. The results suggest that variation of metal levels in cultivated pen shell could be influenced by seasonality and anthropogenic activities such as agriculture and aquaculture developed around the culture zone. Continual monitoring of metals in farmed pen shell is recommended.