Accumulation of Cd, Cu, Pb, and Zn in water, sediments, and mangrove crabs (Sesarma mederi) in the upper Gulf of Thailand

Mangrove crabs (Sesarma mederi) can be used as bioindicators of the environment. This study aimed to estimate the heavy metal content in S. mederi in various Thai mangroves and compare them with other studies for international regulations for human consumption. S. mederi were obtained from the mangroves of the Chao Phraya, Tha Chin, and Mae Klong rivers. The concentrations of Cd, Cu, and Pb in the rivers were low compared to the marine standards of Thailand and estuarine water elsewhere. The concentrations of Cd and Cu in sediments were rather similar to those in other rivers. The results showed that crabs accumulated metals in the order: Cd > Cu > Pb > Zn. The bioconcentration factor of Cd and Cu was highest in Mae Klong, while Pb and Zn were highest in Chao Phraya. Although metal concentrations in crabs were within the ranges found in other studies, they exceeded the maximum ranges according to standards. Hence as mangrove crabs are highly consumed as traditional and international Thai food, they may be a potential health hazard for human consumers. Consequently, the use of mangrove crab could be an interesting tool for monitoring estuary pollution.