Is there evidence of arsenic movement at cattle tick dip sites?

Abstract

Soils at cattle tick dip sites in Australia have been contaminated by a range of chemicals, including arsenic (As). To determine if significant off-site migration of As from dip sites has occurred, 28 dip sites were surveyed to assess both surface and subsurface As transport. Although previous studies using sequential extraction techniques indicated a risk of As leaching at these sites, no evidence of such movement was found in the field from this study.

The As concentration in shallow groundwater (2 m) at clay textured sites was below detection level of 1 μg/L. At sandy textured sites, groundwater immediately adjacent to the dip bath contained significant levels of soluble arsenic, but declined sharply with distance (c. 20 m) from the bath.

The distribution of As at the soil surface was consistent with disposal methods used (pumping out used fluid from the dip). No sites showed significant transport and redeposition of As.

Arsenic speciation in groundwater revealed As ^(V) as the dominant species in all sites. As ^(III) was found in detectable quantities at one site only.

Most dip sites in New South Wales are located on heavier textured soils rich in iron oxides that adsorb As. These sites pose a negligible risk of contaminating groundwater. However, a few dip sites also occur on coastal sand relics. These sites have potential to contaminate groundwater within small distances (c. 20 m) from the dip bath. Lack of significant surface movement of residues was attributed to good vegetation cover at the sites surveyed.