Pollution of agricultural land due to waste disposal from tannery industries

• Tamil Nadu Agricultural University, India

The soil contamination problem addressed by the project was clearly one of considerable importance in Tamil Nadu. In the past, soil Cr contamination has resulted from the disposal of relatively untreated tannery waste to land. Such disposal is no longer undertaken, though disposal of the highly saline effluent and Cr contaminated sludge produced by waste treatment remains a problem.

The tanning and related industries (i.e. goat production) in India employ 2.3 million people, with tanning directly employing 500 000 people. The industry has expanded rapidly with export earnings of around A$6 billion.

In Tamil Nadu State, where 55% of India's tanning industry is located, over 35 000 ha of land have become unfit for agriculture. Pollution from tannery effluent has rendered areas unsuitable for rice and sugar cane, declining by 40% and 80% respectively. The quality of coconuts produced on contaminated land deteriorated, making them no longer commercially viable. Villagers also reported skin rashes from contact with well water. In many areas of Tamil Nadu pollution to groundwater forced villagers to travel 4-5 km for water. Much of this contaminated groundwater became unsuitable for irrigation, and an estimated 600-900 wells in the region fell into disuse.

In India thousands of farmers have lost their farms, or part of their earnings because of contamination by tannery effluents. The objective of this project was to reduce the harmful effects of tanneries by preventing transport of chromium (Cr) and salts from tanneries to surrounding crops, soils and surface and groundwater. The project studied the pathways for dispersion of Cr and salt in the environment, and also devised and tested methods of safe disposal or use of tannery sludge and liquid effluents. It aimed to address issues relating to areas contaminated by historical activity and to the ongoing problem of tannery waste disposal.

This project involved:
establishing facilities and methods of analysis to determine levels of contamination in the wastes, particularly analysis of the differing ionic states of Cr found in soil and groundwater;
characterising a wide range of tannery wastes and soils surrounding tanneries;
tracking the fate of the contaminants in the wastes through detailed site surveys over a two-year period and trialing a small-scale evaporation pond for concentrating effluents;
establishing through glasshouse and field studies a scientific basis for re-using tannery wastes, by growing a range of commercial grass and flower species in treated soil/effluent mixtures subject to a variety of treatments and sludge applications.

Trial plantations of eucalypts, casuarinas and acacias were established using a range of effluent applications. The contaminant levels of plants, soils and groundwater were closely monitored in all trials.

Research in India focused in Tamil Nadu State in close collaboration between staff of the Tamil Nadu Agricultural University and the CSIRO. In Australia, the work focused on the soils and groundwater surrounding old tannery sites in South Australia.

Considerable investment was made by ACIAR, Tamil Nadu Agricultural University (TNAU) and the project teams to establish effective laboratory facilities at TNAU, identify and evaluate appropriate techniques, and develop project staff. This effort was deemed highly effective, with outcomes of lasting benefit to TNAU.

Characterisation of tannery wastes and effluent being produced by Indian tanneries provided a useful baseline to guide further studies, while evaluation of soil Cr indicated the degree of contamination. However, it was impractical to attempt to evaluate the extent of areas contaminated in this manner.

A clear and important outcome from the project was the demonstration of the mobility of Cr in the soil system. This finding clearly indicates that Cr containing tannery waste cannot safely be disposed of to land without risk of contaminating ground and surface waters.

The preliminary studies of plant Cr uptake from tannery sludge amended soils indicated that marked species differences exist. This finding flagged the opportunity to select species for contaminated sites that either do not accumulate Cr or do not translocate it to the harvestable parts. Early studies with non-food crops also showed potential.