Arsenic transfer in water-soil-crop environments of Bangladesh and Australia

• University of Ballarat, Australia
• University of Dhaka, Bangladesh
• Department of Environment and Heritage, South Australia, Australia
• CSIRO Mathematical and Information Sciences, Australia

In many parts of Bangladesh and West Bengal the arsenic concentration in the groundwater extracted from wells and used for human consumption exceeds the World Health Organisation recommended guidelines. As a result, about 4 million people suffer from a degree of arsenic poisoning, and another 40 million are at some risk. The origin of arsenic in this groundwater is unknown. The exposure to arsenic may involve more than just drinking the water or eating food cooked in contaminated water. For some years, the groundwater has been used for irrigating crops. Preliminary studies have shown that vegetables sold at markets in rural Bangladesh may contain arsenic at dangerously high levels.

The situation has worsened in recent years because of the proliferation of wells, often supplied by overseas aid agencies to provide more easily accessible supplies of water in villages. The wells have encouraged the use of groundwater for irrigation of crops, leaving soil increasingly arsenic-rich. People exposed to arsenic over many years suffer from poor health, which then lowers productivity and incomes in affected areas, leading to further problems.

The purpose of this project was to understand the pathways by which arsenic is consumed by the human population in order to prevent further cases of arsenic poisoning, by investigating the extent of arsenic contamination in selected districts of Bangladesh, India and Australia. Strategies to reduce the exposure of people and animals to the poison were also to be devised.

The scientists assessed the extent of soil contamination, measured the arsenic concentration in crops, and evaluated the relative importance of the various pathways of arsenic ingestion to see what was the most significant for the population. The project was divided into two phases: in the first phase staff were trained in relevant scientific knowledge and techniques in Ballarat and Bangladesh. Researchers and technicians then characterised the soils and groundwater across a range of sites, measuring arsenic concentration in soil and water as well as crops and animal fodder. The study included areas of Australia known to be contaminated.
Glasshouse studies investigated the ability of plants to take up and concentrate arsenic from both soil and water. The scientists tried to determine the long-term fate of arsenic in farming areas affected by contaminated groundwater in Bangladesh, and in Australia by episodes of contamination such as sheep-dip sites or from mining. The final part of the project estimated the risk exposure factors for affected populations, and developed strategies for minimising arsenic contamination in future and dealing with areas already contaminated.

Considerable progress was made towards the understanding of arsenic transfer in water-soil-crop environments of Bangladesh and Australia. Analytical and sampling strategies were developed to characterise soil, water and plant samples from arsenic-contaminated sites in both Australia and Bangladesh. The extent and severity of arsenic pollution was determined in selected districts of Bangladesh, along selected disused railway corridors in South Australia, and in the Goldfields area of Victoria.

In Bangladesh, crops receiving arsenic-contaminated irrigation water were shown to take up this element and accumulate it in different degrees, depending on the plant species and variety. Green leafy vegetables, particularly Arum, act as arsenic accumulators.

In Australia, it was shown that plants collected from along the former railway corridors in South Australia, and within the Goldfields area, could contain elevated levels of arsenic. Some arsenic-contaminated soils can reduce plant yields dramatically.

Glasshouse studies demonstrated that plant arsenic uptake is influenced by soil solution arsenic concentration and soil pH. There was evidence that arsenic 'ages' over time in contact with the soil and this reduces its availability to plants. Preliminary estimates suggest that, besides drinking water, the food chain can represent a significant pathway of arsenic ingestion by the human population in Bangladesh (40% of arsenic transferred by the food chain). Some preliminary work was undertaken on management strategies for reducing risk of arsenic ingestion by the Bangladesh farming community.

Laboratory facilities and arsenic research groups were established at the University of Dhaka and Ballarat University, and research and technical staff in Adelaide, Ballarat and Bangladesh received training.

Not all the original objectives of the project were fully met. The project was extended to enable further glasshouse studies and field work on arsenic uptake by vegetables to be carried out, in order to complete the data set required for developing risk assessment and risk management strategies.