organoarsenic feed additives used in the swine farming in the
CAFO zone. The net accumulation of arsenic in soil (109.5 tonnes)
is less than the estimated input (126 tonnes), probably because
significant fractions of the arsenic species (primarily in the forms
of arsenate and arsenite) had been leached out of the surface soils
by rainwater and irrigation water, which subsequently impacted
local surface water and groundwater. Therefore, the extensive
use of organoarsenic feed additives makes animal wastes a significant
anthropogenic source of arsenic pollution in the CAFO zone.
The ecological risk index (Er) values calculated for arsenic in the
surface soils of the CAFO zone are all lower than 40 (data not
shown), indicating low to moderate potential ecological risk
(Hakanson, 1980). Nonetheless, with the continuous expansion of
swine farming industry in the CAFO zone, fast accumulation of
arsenic from the animal wastes can significantly raise the potential
ecological risk of arsenic pollution in the near future if no action is
taken to limit the use of organoarsenic feed additives in intensive
animal farming.