Residues of DDTs, PAHs and some heavy metals in fish (Tilapia) collected from Hong Kong and mainland China.

Most of the freshwater fish consumed in Hong Kong is imported from the southern part of China, although Hong Kong also produces a small amount of freshwater fish. The major aim of the present study was to conduct a health risk assessment of fish produced from the mainland (purchased from four local markets in Hong Kong) compared with those produced from Hong Kong fishponds. Thirty tilapia fish (Tilapia mossambicus) were collected from the fishponds at Tam Kon Chau, Nam Sang Wai, and Mai Po Nature Reserve (Northwest New Territories of Hong Kong), and four local markets (Tai Po, Lok Fu, Sham Shui Po and Cheung Sha Wan wholesale markets) in Hong Kong for the analyses of PAHs, DDTs and three toxic metals (cadmium, chromium, lead). Tilapia purchased from the markets (with fish supplied from the mainland) showed higher concentrations of DDTs and PAHs than those collected from Hong Kong fishponds, confirmed that the fishponds in the mainland are more polluted due to the rapid socioeconomic growth in the region during the past 20 years. The tilapia were heavily polluted by Pb, with the highest level (3519 ng g-1 wet wt.) exceeded the EUROPA guideline (400 ng g-1 wet wt.) 8 times, and Cr with 36% of the samples exceeded the China guideline of 500 ng g-1 wet wt. for human consumption. The coastal Chinese populations which consume larger quantities of fish may be at risk. Tilapia collected from the Mai Po Nature Reserve contained the highest level of Cr, which may also impose adverse effects on water birds, including the endangered species that frequently visiting the site for food and shelter.