Peter Chawaga reports that in the U.S., arsenic concentrations in excess of the drinking water maximum contaminant level (MCL) of 15 mg/l in groundwater from public wells are distributed across the U.S., but 75% of these wells are in the western U.S., said Babur Mirza, a member of the research team. In basin-fill aquifers in California, Nevada, New Mexico, Arizona, and Utah, 10% of domestic wells sampled had arsenic in excess of the MCL. The Cache Valley Basin is located 128 kilometers northeast of Salt Lake City. A survey of domestic wells in this basin showed that 17% of the 161 wells sampled had arsenic in excess of the MCL. To help combat arsenic in water supplies, the researchers wanted to attack it at its source. They saw an opportunity to help by providing a better system for identifying the bacteria that transform arsenate into arsenite, the toxic substance that infiltrates groundwater and leads to widespread contamination.
Inorganic arsenite is readily soluble in water and, because the ion it forms in water is negatively charged, it does not bind well to soil particles, said Mirza. It has a much higher acute toxicity than arsenate. The researchers developed a strand of DNA known as a primer. The primer identifies arsenate respiratory reductase (arrA), the gene that turns arsenate into the more toxic arsenite. These primers are designed specifically to target the arsenate reductase gene, Mirza said. If a microorganism does not have this gene, none of its DNA will be amplified in the polymerase chain reaction where the primers are employed. The researchers designed the primer based on DNA nucleotide sequences from the National Institute of Health GenBank database, an annotated collection of all publicly-available DNA sequences. The team extracted DNA from several soil and groundwater samples, using the primer to amplify the gene and then sequencing the amplified DNA to make sure it was identical to what it that from the GenBank.
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