In contrast, animal wastes are the predominant
form of fertilizers used in the CAFO zone due to their ready availability
and the short transportation distance required. The correlation
between the contents of arsenic and organic carbon in the
surface soils from the CAFO zone suggests that the fertilization of
agricultural lands with animal wastes was a likely source of arsenic
in the surface soils. The r2 value of the linear model in the CAFO
zone is small because lithogenic materials remain the predominant
source of arsenic in the soils. As discussed earlier, the mean content
of soil arsenic (16.0 mg kg1) was not too much higher than
that (12.2 mg kg1) in the agricultural soils in the Pearl River Delta,
thus TOC in the surface soils could not be the only predictor for soil
arsenic content, even if the soil organic matter came completely
from the animal wastes