Fractionation and ecological risk of metals in urban river sediments in Zhongshan City, Pearl River Delta

Abstract

Surface sediments collected from nine urban rivers located in Zhongshan City, Pearl River Delta, were analyzed for total concentration of metals with digestion and chemical fractionation adopting the modified European Community Bureau of Reference (BCR) sequential extraction procedure. The results showed that concentration and fractionation of metals varied significantly among the rivers. The total concentration of eight metals in most rivers did not exceed the China Environmental Quality Standard for Soil, Grade III. The potential ecological risk of metals to rivers were related to the land use patterns, in the order of manufacturing areas > residential areas > agriculture areas. The concentration of Pb in the reducible fraction was relatively high (60.0-84.3%). The dominant proportions of Cd, Zn and Cu were primary in the non-residual fraction (67.0%, 71.8% and 81.4% on average respectively), while the percentages of the residual fractions of Cr and Ni varied over a wide range (43-85% and 24-71% respectively). The approaches of the Håkanson ecological risk index and Secondary Phase Enrichment Factor were applied for ecological risk assessment and metal enrichment calculation. The results indicated Hg and Cd had posed high potential ecological risk to urban rivers in this region. Meanwhile, there was widespread pollution and high enrichment of Cu in river sediments in this region. Multiple regression analysis showed that five water quality parameters (pH, DO, COD(Mn), NH(4)(+)-N, TP) had little influence on the distribution of metal fractionation. This result revealed that the ecological risk of metals was not eliminated along with the improvement in water quality. Correlation studies showed that among the metals, Group A (Cd, As, Pb, Zn Hg, r = 0.730-0.924) and Group B (Cr, Cu, Ni, r = 0.815-0.948) were obtained, and the metal contaminations were from industrial activities rather than residential.

Speciation and ecological risk of heavy metals and metalloid in the sediments of Zhalong Wetland in China

“…The speciation of heavy metals provides critically important information for evaluating toxicity and ecological risk to animals and human (Fan et al 2008;Kwon and Lee 2001). Different chemical species of heavy metals have different activity, toxicity, and mobilization (Cai et al 2011;Lu et al 2010;Zheng et al 2013). The changing environment can also result in the transformation of heavy metals between particulate forms and dissolved form (Teasdale et al 2003;Yu and Hu 2008).…”

“…The classification is based on the strength of the bond between metals and the different geochemical fractions in sediments and the ability of metals to be released (Cai et al 2011) and enter into the food chain. The carbonate and exchangeable fractions are considered to be weakly bonded metals, which may equilibrate with the aqueous phase and become more rapidly bioavailability (Hseu 2006;Yan et al 2010).…”

Fractionation and ecotoxicological implication of potentially toxic metals in sediments of three urban rivers and the Lagos Lagoon, Nigeria, West Africa

“…A predominance of relatively labile Pb species has been previously reported in the Pearl River (Li et al 2007;Cai et al 2011) where it was attributed to current anthropogenic inputs. Similarities were also found between fractionation patterns for Zn in the current study and in rapidly urbanising areas in China, with > 50% of the analyte released from most samples in the first two steps of the BCR extraction (Cai et al 2011;Qiao et al 2013).…”

“…A predominance of relatively labile Pb species has been previously reported in the Pearl River (Li et al 2007;Cai et al 2011) where it was attributed to current anthropogenic inputs. Similarities were also found between fractionation patterns for Zn in the current study and in rapidly urbanising areas in China, with > 50% of the analyte released from most samples in the first two steps of the BCR extraction (Cai et al 2011;Qiao et al 2013). In contrast, Cu, Cr, Pb and Zn in sediments from the largest tropical lagoon in India, Chilka lake (Panda et al 1995) were dominantly associated with the residual fraction, suggesting that, at least in the mid 1990's when the study was conducted, the system was relatively unaffected by anthropogenic input.…”

“…The application of sequential extraction to provide insight into PTM geochemistry in estuaries, Iyaalaro sites 5 and 6; Cr was generally found in relatively immobile forms; whilst Cu showed variable fractionation, sometimes being found mainly associated with more labile phases (Cai et al 2011) and sometimes mainly with oxidisable and residual phases (Canuto et al 2013;Chen et al 2010;Yan et al 2010). A predominance of relatively labile Pb species has been previously reported in the Pearl River (Li et al 2007;Cai et al 2011) where it was attributed to current anthropogenic inputs.…”