Fig. 2. Arsenic contents and pollution levels in the surface soils from the CAFO zone and in the surface soils from the agricultural lands in the Pearl River Delta: (a) distribution
histograms of soil arsenic contents (data outliers, i.e., values smaller or larger than 1.5 times the interquartile range, have been removed), and (b) distribution of soil pollution
level. Agriculture soils are classified into four categories based on the arsenic contents: Class I (40 mg kg1) based on the Environmental Quality Standard for Soils in China (SEPA, 1995). Class I soils are regarded as unpolluted.