3.3. Arsenic species in environmental matrices of the CAFO zone
The chemical forms of the arsenic compounds in the surface
soils, and in the samples of surface water and sediment as well,
were analyzed to further assess the contributions from the organoarsenic
feed additives. Table 3 summarizes the concentrations of
six arsenic species, including inorganic arsenic [As(III) and As(V)],
common organoarsenic compounds found in the environment
(MMA and DMA), and organoarsenic feed additives (ASA and
ROX) in the environmental matrices of the CAFO zone. It should
be noted that the total amount of arsenic species extracted by
the 0.5 M H3PO4 is much less than the total arsenic in the soil
and sediment samples determined by total digestion. This is not
surprising, as inorganic arsenic is primarily present within the
matrices of soil and sediment minerals and this fraction is not
extractable by weak acids, while the results of total digestion
include this fraction (Zhang et al., 2012a). On the other hand, the
fractions of arsenic species extracted by 0.5 M H3PO4 could closely
represent those that are potentially bioavailable and pose environmental
risk. Therefore, the results for soil and sediment samples
summarized in Table 3 could reflect more accurately the fractions
introduced by external sources and are bioavailable compared to
total arsenic contents. Arsenate was found to be the major inorganic
arsenic species, while ASA was the major organoarsenic species
in the surface soils and sediments.