Temporal and spatial distribution of heavy metal contamination in Gaohong, Lin'an, Zhejiang Province

Abstract

Gaohong, a small town situated at the west of Hangzhou, is one of the largest production bases of compact fluorescent lamps (CFLs) in China. To determine the influence of local CFL production on temporal and spatial distribution characteristics of heavy metals in ambient bamboo forest soils during the four seasons, a systematic survey was conducted in March, July, and October of 2012 and January of 2013 with a total of 272 soil samples collected at 17 sampling sites in CFL production areas. Each sampling site was 8 m×8 m, on which four topsoil samples (0-10 cm) per time were collected by a soil auger in the diagonal position. Each sample's representativeness was ensured by collecting four field replicates in a one-meter diameter area and then mixed together as one sample. The chemical properties and heavy metals contents of the samples were determined, and the spatial and temporal distribution characteristics of heavy metals in soils was elucidated using descriptive and cluster analysis. Results showed that the average pH value of the bamboo forest soils was 5.55, and the mean organic matter content was 53.00 g·kg-1. The highest value for Hg was 0.61 mg·kg-1, two times higher than the Environmental Threshold for Agricultural Soil (HJ/T 332-2006) and the Grade Ⅱ Standard of Soil Environment Quality in China (GB 15618-1995). Spatial variability of the heavy metals was in an order of Hg > As > Zn > Se > Cu > Ni > Cr > Pb > Cd. After eliminating outliers, the heavy metals, except Ni, were non-normally distributed. The cluster analyses showed that there was a significant mutually associated compound contamination property between Zn and Pb, Ni, Cu, and Cr (P < 0.01), while Hg and the other heavy metals (Zn, Pb, Cu, Cr, Ni, As, Se, and Cd) might have originated from different sources. Thus, even though these acidic bamboo forest soils with abundant organic matter had been polluted by mercury, an essential raw material for the CFL industry, and even though heavy metal contamination had possibly been induced by anthropogenic activities, it was possible that Zn, Pb, Cu, Cr, Ni, As, Se, and Cd in the bamboo soils did not originate from the CFL industry.