Arsenic contamination of soil and groundwater from the leaching of CCA treated fence posts in several Hawke's Bay vineyards

Abstract

Throughout the rapidly expanding area of vineyards in New Zealand, great numbers of wooden posts, treated with copper, chromium and arsenic (CCA) are used to support the vine canopy. Studies have shown that when CCA-treated wood remains in the ground, varying amounts of copper, chromium and arsenic leach into the surrounding soil. Arsenic is particularly toxic, so any contamination of soil or groundwater is of concern. Therefore, it is important to determine the extent of arsenic accumulating in soil surrounding treated posts and the mobility of arsenic in soil, to investigate the potential for groundwater contamination.

Soil samples were taken at several depths and distances from 35 post locations throughout several vineyards in the Hawke's Bay region to determine the extent and mobility of arsenic in soil. At each vineyard and several control sites, groundwater samples were taken from existing wells to examine any groundwater contamination. Analyses of soil samples showed all thirty five post sites to have elevated concentrations of arsenic. Arsenic was found to accumulate in greater concentrations in soils with a higher organic matter and clay content, and a lower sand content, while arsenic was found to be more mobile in the soil profile, both vertically and laterally, in the more acidic soils that contained higher sand contents and lower organic matter contents. No groundwater samples contained elevated levels of arsenic. Results suggest that arsenic accumulation in vineyard soils is widespread, and in the right conditions can be mobile in the soil profile. While no groundwater samples contained elevated arsenic levels, it is not known how long it may take for arsenic to travel into groundwater so monitoring of groundwater quality is needed in the future. Mitigation measures such as using alternatives to CCA treated posts, and disposal methods for broken and unwanted posts, are required to reduce the possible impact on the environment.