Mytilus californianus as an indicator of heavy metals on the northwest coast of Baja California, Mexico

Samples of Mytilus californianus were analyzed to determine the spatial and temporal distribution of Ag, Al, Cd, Cr, Cu, Mn, Pb and Zn concentrations on the northwest coast of Baja California and to compare the results with levels reported for California, USA. The samples were collected at eight sites from the US–Mexican border to San Quintín, BC (300 km south of the border) in February and July 1982 and 1994. During both years, north–south gradients in the concentration of Ag and Pb were observed, with the highest values close to the US–Mexican border (Ag=0.60–1.54 and Pb=0.21–2.89 μg g−1) and the lowest in the southern part of the study area (Ag=0.05–0.10 and Pb=not detectable–0.03 μg g−1). The Ag and Pb gradients suggest that their distributions are affected by anthropogenic activities close to the US–Mexican border. South–north gradients in the concentration of Cd (minimum=0.59–2.16 and maximum=2.61–12.93 μg g−1), for both 1982 and 1994, were observed. The geographic annual means of Pb for California (average of six stations along the entire state) were significantly higher than those of this study (average of the eight sampling sites) in 1982 and 1994. Cu in California was significantly greater than that of this study only in 1994. Cluster analyses on all metals indicate three similar geographic zones in 1982 and 1994, suggesting a relative consistency in the processes that determine the spatial variability of the concentration of some metals in M. californianus on the northwest coast of Baja California.