An overview of waste water utilization, its impacts and management of soil-plant continuum in peri-urban agriculture

The increasing population growth, rapid industrialization and urbanization around the peri-urban areas of West Bengal, India have caused serious ecological problems. The indiscriminate disposal of domestic wastes, municipal sewage water and industrial effluents by numerous municipalities and industries onto adjoining open agricultural lands and surface water bodies and subsequent use of this nutrients and metals rich waters for crop irrigation for longer duration by the resource poor local farmers led to the contamination of the valuable natural resources like soil, water and plant and adversely affected the economic yield and quality of crop. These metals enriched plants are most hazardous to mammals and human health after intruding their biological system through food web. With a view to assess the quality of waste waters and the impacts of the heavy metal contents in the prevalent soil, water and crop resources adjoining to the industries and municipalities around the major cities of West Bengal, an extensive field and laboratory based investigations and literature survey works were undertaken. The identified areas prioritized were the agricultural lands adjacent to the Kolkata municipalities, Dankuni Industrial Complex and Durgapur industrial belt. The soil, water and plant samples were collected from the same contaminated sites receiving long-term irrigation through sewage waters and effluents from municipalities and industries of various categories, urban waste refusals, domestic and animal wastes and heavy traffic-road wash. The concentrations of toxic heavy metals viz., Cd, Cr, Ni, Pb and Co in soils varied widely and were above the permissible limits. The corresponding figures for these pollutants in different water bodies were well below the toxic limits and constituted only a small fraction compared to soil counterparts. However, their long-term application in the farmlands appeared to build-up the toxic concentrations in soils and ultimately become hazardous to crops grown thereon. The plant uptake of metals was several folds higher than that in the soils and water bodies. However, metal concentrations and accumulations were exceptionally higher in vegetable plants than in cereals, oilseeds and fodder crops. This implies the crop preference for selective absorption of metals from the soils is function of crop species and varieties. These crops were not qualitatively fit for consumption as metal contents in these plants were above the permissible limits. This indicates the danger of entry of toxic metals into the food web via soil route along with its possible biomagnifications through crop intake. On repeated ingestion of these metal-rich crops would likely to be hazardous to animal and human health in course of time. Some remedial measures and suggestions are being made to use these contaminated soils and waste water for crop cultivation in view of shrinking land and water resources. Initiation of awareness programme among the farming community and strengthening the existing laws, regulations and acts for various contaminating agencies are advised.