Toxicity and profitability of rice cultivation under wastewater irrigation: the case of the East Calcutta Wetlands

The paper reports the results of an empirical study on profitability of rice cultivation in the East Calcutta Wetlands (ECW) region where untreated sewage from the city of Kolkata (earlier Calcutta), India, is used for the purpose of irrigation during the winter/summer crop. The results show that plots using wastewater containing organic nutrients earn lower profits than those using groundwater. We also find that the profitability of plots using wastewater is negatively affected by the presence of heavy metals such as Lead and Mercury that are carried through untreated sewage-water canals and deposited in the soil. Of the two opposing effects of wastewater irrigation, the negative effect of heavy metal toxicity outweighs the positive effects of organic nutrients. The results support regulation of the discharge of the heavy metals like Lead and Mercury into the wastewater from households and industries. This would lead to conservation of the Wetlands generating a number of ecological and environmental benefits to the society.