Use of organoarsenicals as pesticides may lead to contamination of soils and groundwater with toxic arsenic species
The impact of extensively used arsenic-containing herbicides such as monosodium methanearsonate (MSMA) on groundwater beneath golf courses has become a topic of interest. Although the currently used organoarsenicals are considered to be less toxic, their application into the environment may produce the more toxic inorganic arsenicals.
This is the result of a recent field test that was established at the Fort Lauderdale Research and Education Center (FLREC), University of Florida . In this study, percolate water was collected after MSMA application for speciation and total arsenic analyses. The results showed that the substrate composition significantly influenced arsenic mobility and arsenic species transformation in the percolate water. Arsenic species transformation occurred in soil, resulting in co-occurrence of four arsenic species, arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in percolate water.
This result is of real concern, since the arsenic accumulates over the years of application in the soil and creates an inventory that might become an important source for groundwater contamination in the future. Ma et al.  compiled the arsenic soil concentration data from FDEP reports for 11 golf courses in Florida. The average arsenic concentration value reported in this study was 69.2 mg/kg with a range of 5 to 250 mg/kg. Cai et al.  studied the mobility of the arsenic in the soil of golf courses. These researchers found that the extractable arsenic was in the range of ~ 30% .
Unfortunately the use of arsenic pesticides is not only historically relevant  but continues in some countries. The biggest consumers of arsenic in the world is the US, which alone has imported about 24,000 metric tons of arsenic in 2000 . While the main use has shifted from pesticides to CCA wood preservation, the total amount of arsenic brought into the environment has not been reduced significantly since the 1940's, when consumption peaked at more than 30,000 tons. Altogether, about 1.6 million tons have been spread since 1910 in the US. Of this quantity roughly two-thirds has been used for the production of agricultural arsenical pesticides and roughly one-third has been used for arsenical wood preservatives.
The 1.6 million metric tons is significant. Spread homogeneously over the entire surface of the USA, this amount would be capable of increasing the concentration of a soil volume equivalent to the upper 1 inch of U.S. land by almost 4 mg/kg; it is capable of increasing the concentration by 50 µg/L for a volume of water equivalent to covering the entire U.S. with 3.3 meters (11 feet) of water. Similarly, the volume of water over the U.S. land area would be 17 meters (55 feet) deep for a concentration increase of 10 µg/L . The 50 µg/L corresponds to the existing federal drinking water compliance-standard for arsenic. The 10 µg/L corresponds to the compliance standard that will take effect in 2006.
Such numbers should well demonstrate that significant impact of projects to clean-up drinking water resources or remediation of contaminated sites cannot be achieved without blocking such ongoing contamination.
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