New guidelines controlling the disposal of tannery effluent have been introduced by pollution control authorities in India. The guidelines are based on scientific analysis and results from an ACIAR supported project on tannery waste.
The project, Pollution of agricultural land due to waste disposal from tannery industries, characterised tannery wastes and effluent produced by Indian tanneries. These investigations revealed extensive chromium contamination of soils, surface water and groundwater.
In Tamil Nadu state where more than 60% of India’s economically important tanning industry is located, tannery waste containing chromium and sodium compounds has, over many years, contaminated 55 000 ha of agricultural land. Thousands of farmers lost their farms, or part of their earning capacity through this contamination.
In many areas of Tamil Nadu, groundwater now cannot be consumed, forcing villagers to travel 4–5 km for water. Much of the groundwater is unsuitable for irrigation, and hundreds of wells in the region can no longer be used.
Under the project, modern laboratory facilities were established at Tamil Nadu Agricultural University and staff trained in their use. Using these facilities, researchers characterised tannery wastes and effluent produced by Indian tanneries. Investigations in Tamil Nadu and near Adelaide revealed extensive chromium contamination of soil, surface water and groundwater.
Soils sampled near tanneries in the Vellore area of India had chromium concentrations of up to 7% (70 000 mg/kg). Tannery sludges used in agriculture also have high chromium concentrations (up to 4% on a dry solids basis). Effluent treatment before disposal (as is now mandatory) produces chromium-rich sludges that are often used as soil additives for agricultural food crops, without information on the availability of the chromium to plants and mobility of chromium in soil.
An important outcome was demonstration of the mobility of chromium in the soil system. This had not previously been reported, and indicates that chromium-containing tannery waste cannot safely be disposed of to land without risk of contaminating ground and surface waters.
Water sampled from borewells located 2 km from a closed tannery at Walajapet had exceptionally high chromium content (more than 950 µg/L); a typical background value in many regions of India is 4–7 µg/L. And more than 80% of chromium was present as the toxic hexavalent form.
Remediation of soils contaminated with chromium will not only will help sustain agriculture but will also minimise adverse environmental impacts. Studies of chromium uptake by plants growing in soils amended with tannery sludge revealed marked differences between species, raising the prospect of selecting species that do not accumulate chromium, or do not move it to harvested parts.
Non-food crops also showed potential, as did revegetation with tree plantations and flower crops tolerant of chromium and salt.
Guidelines proposed by the researchers identified critical factors that existing industries need to consider before disposing of their wastes, and stressed that environmental impact assessment is necessary before new industries are established. The guidelines included water table depth, and characteristics of the waste, including odour, total chromium content, chemical and biological oxygen demand, nitrate, phosphate, sodium, chloride and heavy metals such as cadmium and arsenic.