PCBs equivalent to Aroclor 1242 and 1254 in soft tissues of oysters Crassostrea rivularis from the Guangdong coast, China, were measured using a GC-ECD. PCB concentrations (ngg⁻¹d.w.) ranged from 30 to 2040 with an average of 315 in 2003–2007, and 0.35–1.43 with an average of 0.56 in 1989–1991. Annual averages were 0.61, 0.65, 313, 290 and 342ngg⁻¹, respectively in 1989, 1991, 2003, 2006 and 2007. In east Guangdong, the Pearl River Estuary, and west Guangdong, regional means were 444, 273, 194ngg⁻¹, respectively in 2003–2007, and 0.43, 0.78, 0.38ngg⁻¹, respectively in 1989–1991, indicating PCB levels in oysters have risen greatly by ratios of 350–1032 compared with earlier data. PCB sources may derive from older transformers, printing materials and pressworks. Fortunately, current residual PCBs in the oysters were 0.004–0.253mgkg⁻¹ (w.w.), still below hygienic criteria of China and developed countries.

Long-term spatiotemporal trends and health risk assessment of oyster arsenic levels in the coastal waters of northern South China Sea were investigated in order to help improve the quality and safety control and sustainable aquaculture for mollusks in China. Cultured oysters (Crassostrea rivularis) collected from the waters of 23 bays, harbors, and estuaries along the coast of northern South China Sea from 1989 to 2012 were examined for spatial patterns and long-term temporal trends of oyster arsenic levels. Single-factor index and health risk assessment were used to quantify arsenic exposure to human health through oyster consumption. Overall, arsenic was detected in 97.4% of the oyster samples, and oyster arsenic levels were non-detectable—2.51 mg/kg with an average of 0.63 ± 0.54 mg/kg. Oyster arsenic levels in the coastal waters of northern South China Sea showed an overall decline from 1989 to 2012, remained relatively low since 2005, and slightly increased after 2007. Oyster arsenic levels in Guangdong coastal waters were much higher with more variation than in Guangxi and Hainan coastal waters, and the long-term trends of oyster arsenic levels in Guangdong coastal waters dominated the overall trends of oyster arsenic levels in the coastal waters of northern South China Sea. Within Guangdong Province, oyster arsenic levels were highest in east Guangdong coastal waters, followed by the Pearl River estuary and west Guangdong coastal waters. Single-factor index ranged between 0.27 and 0.97, and average health risk coefficient was 3.85 × 10⁻⁵, both suggesting that oyster arsenic levels in northern South China Sea are within the safe range for human consumption. However, long-term attention should be given to seafood market monitoring in China and the risk of arsenic exposure to human health through oyster consumption.

Coastal heavy metal pollution has become an important topic for seafood safety and marine environmental protection. Unlike toxic heavy metals such as cadmium or chromium, copper is essential for oysters’ growth but can inhibit their immune response to exotic stress when going above normal levels. Oysters with high copper levels can easily accumulate and transfer abnormal amounts of copper to upper trophic levels, and generate health risks for humans. This study investigated the spatiotemporal variability and health risk of copper levels in cultured oysters (Crassostrea rivularis) sampled from 23 harbors, bays, or estuaries along the northern South China Sea during 1989–2015. Overall, oyster copper concentrations in the study area ranged from 0.9 to 1897.0 μg/g wet weight with a mean of 210.0 (± 143.6) μg/g and a median of 89.3 μg/g. Although oyster copper levels in the southern China provinces of Guangdong, Guangxi, and Hainan showed an overall decrease during 1989–2015, they stayed relatively low since 1996 and increased slightly after 2010. Oyster copper levels in Guangdong were significantly higher than in Hainan and Guangxi. In Guangdong, oyster copper levels were highest in the Pearl River Estuary, followed by west Guangdong and east Guangdong. The health risk of copper exposure through oyster consumption increased in 2011–2015 compared with in 2006–2010. It is recommended that the human daily intake of cultured oysters in the study area should be reduced by half to minimize copper exposure. This study suggested that copper is one of the most important heavy metal contaminants in coastal and estuarine ecosystems of the northern South China Sea.

The distribution of the toxic elements As, Cd, and Pb in nine different types of seafood from Shenzhen, China, was investigated by using inductively coupled plasma mass spectrometry (ICP-MS). The results revealed that the concentrations of arsenic (As) in fish (Lutjanus erythropterus, Paralichthys olivaceus) and in bivalve (Meretrix meretrix) and cadmium (Cd) in scallop (Argopecten irradians) exceed the limits established by food safety regulations in China and EU (European Union). Furthermore, the bioavailability of As, Cd, and lead (Pb) in mice after 20-day oral ingestion of Crassostrea rivularis was investigated, and the total rate of absorption of toxic elements in samples from the liver and kidney tissues and blood was determined. The results of this in vivo trial indicated that the oral bioavailability of As, Cd, and Pb was approximately 0.33, 0.45, and 0.74%, respectively.