Seasonal characteristics of cadmium content and distribution in Pearl River estuary

Seasonal characteristics of cadmium were studied in the Pearl River estuary from February to November,2008,including distribution of cadmium in water bodies,sediments and aquatic animals.For water samples,1L water was collected from 0.5 m below surface and fixed with 2 mL hydrogen nitrate.For sediment samples,the surface bottom mud was collected with grabtype sediment sampler and saved in sealed bag.For organism samples,we just selected muscle of the fish and shrimp and saved different species in its own sealed bag.The above sam-pling processes were all in accordance with The Specification for Marine Monitoring.The water samples were processed with resolution method according to National Standard(GB/T 7457-87) and the sediment samples were also processed with resolution method according to National Standard(GB/T 17137-40 1997).The mud was treated in the following sequence: cleared off sundries,air-dried,and grinded.The homogenate of organism mus-cle was processed according to National Standard(GB/T5009-2003).All the processed samples were detected with flame atomic absorption spectrophotometer(Varian SpectrAA 400).Our results indicated that the cadmium con-centration in water bodies ranged from 0.022 mg/L to 0.047 1 mg/L,with an average of 0.012 8 mg/L.The highest value appeared in February,while the lowest value appeared in August,with the sequence of February,May,No-vember and August.According to the Environmental Quality Standards for Surface Water GHZBI,our results showed that water quality of the studied area was worse than Class III water quality standards.The cadmium con-centration in sediments ranged from 5.062 mg/kg to 9.239 mg/kg,with an average of 6.974 mg/kg,which was higher than those in other estuarine areas,and showed a steady increasing trend.The cadmium concentrations in aquatic animals ranged from 0.144 mg/kg to 0.430 mg/kg,which were higher than the national limiting standard.Furthermore,the cadmium concentration in predatory fish was relatively higher than that in omnivorous fish.Compared with previous studies in Pearl River estuary,we found an apparent increasing trend for cadmium con-centration in fish bodies during recent years.