16 February 1996 Lincoln scientist adds to knowledge of major soil contaminant

ARSENIC that valuable industrial chemical as well as the sinister substance of many a murder mystery, is under the spotlight these days as a major environmental contaminant. In Australia, old cattle tick dipping sites are the focus of concern. In New Zealand it's former timber treatment locations. Now, the work of a Lincoln University soil scientist, working with Australia’s Commonwealth Scientific and Industrial Research Organisation has led to the development of new techniques for assessing the extent and nature of problems associated with arsenic­ contaminated sites.

Working with the CSIRO for six months last year on a McMaster Research Fellowship, Soil Science Reader Dr Ron McLaren developed an "arsenic fractionation" method of examining the forms of arsenic in the soil.

Ticks pose a multi-million dollar threat to the cattle industry in Australia and historically they have been controlled by putting stock through dips containing arsenical compounds and the organochlorine pesticide DDT. Although the use of these chemicals was phased out during 1955-62, both are known to persist in the soil around thousands of cattle dip sites throughout Australia.

The overall project to which Dr McLaren contributed investigated arsenic chemistry in soils in relation to understanding soil conditions which control the solubility, mobility and bioavailability of arsenic. The aim was to develop soil test procedures to help predict hazardous levels in terms of water quality and bioavailability and to model the movement of arsenic from contaminated sites.

Dr McLaren's own part within this project was the development of procedures to examine the forms of arsenic in soil and to identify the various species of arsenic in soil solution.

To assess the nature and potential mobility of the arsenical compounds in soil at the dip sites, Dr McLaren and his team developed a sequential chemical fractionation method. The scheme identifies six different soil arsenic fractions with varying degrees of reactivity.

In addition to developing this scheme, a new method was examined for determining the chemical forms of arsenic in soil solutions.

"With many types of soil contaminant, there is still a need for a lot of research concerning both the exact nature of the problem and how to overcome it," says Dr McLaren.

"This is particularly true for heavy metal and organic chemical contaminants, but with arsenic we have now certainly made a start.

"The Australians are committed to action on their old contaminated cattle dipping sites and in New Zealand we can now use the arsenic fractionation scheme developed in New South Wales to examine the fate of arsenic in soils affected by timber treatment solutions."

The Community Diary. Produced by The Community Relations Centre, Lincoln University, Canterbury, New Zealand