We assessed the spatiotemporal trends
of the concentrations of
11 heavy metals (HMs) in the liver and kidney of Indo-Pacific humpback
dolphins (<i>Sousa chinensis</i>) from western Pearl River
Estuary (PRE) during 2004–2015. The hepatic levels of Cr, As,
and Cu in these dolphins were among the highest reported for cetaceans
globally, and the levels of Zn, Cu, and Hg were sufficiently high
to cause toxicological effects in some of the animals. Between same
age-sex groups, dolphins from Lingdingyang were significantly more
contaminated with Hg, Se, and V than those from the West-four region,
while the opposite was true for Cd. Generalized additive mixed models
showed that most metals had significant but dissimilar temporal trends
over a 10-year period. The concentrations of Cu and Zn increased significantly
in recent years, corresponding to the high input of these metals in
the region. Body-length-adjusted Cd levels peaked in 2012, accompanied
by the highest annual number of dolphin stranding events. In contrast
to the significant decrease in HM levels in the dolphins in Hong Kong
waters (the eastern reaches of the PRE), the elevated metal exposure
in the western PRE raises serious concerns
