Pollution of Coastal Water
The existing land use pattern of coastal belt of West Bengal reveals that important sectors like agriculture constitute about 1348 square kms.; mud flats and beach cover about 200 square kms., coastal aquaculture impoundment 267 square kms., saltpans and salt marsh 28.6 and 22.13 square kms, respectively. The forest area covers 1952 square kms. of actual dense mangrove zone within the Coastal Regulation Zone I of 4164 square kms. Major sources of pollution in the coast of West Bengal are wastewater generated from domestic, agricultural and industrial activities. Status of these discharges and their load into coastal waters are detailed below.
Major sources of domestic waste in the state are the busy coastal towns and tourist resorts namely Digha, Haldia, Kakdwip, Bakkhali, Diamond Harbour,Canning and Basanti from which substantial quantity of municipal waste, totally untreated, find their way into coastal sea throughout the year either directly or indirectly through creeks/canals and estuaries. As per estimates of CPCB, around 785.4 MLD sewage is generated from cities and town in West Bengal of which only around 141.7 MLD is treated and balance is discharged into coastal waters untreated. This translates into discharge of around 146 and 378 TPD of BOD and COD respectively into the coastal waters. It is estimated that municipal waste to the tune of about 400 tonnes of sewage every day from Kolkata metropolis is discharged into coastal waters of Sundarban..
Oil wastes in water bodies
Operational activities at port (Haldia), shipping discharge, discharge from major fish centres at Sankarpur and Namkhana and also from mechanized fishing and cargo boats form some sources of residual oil, grease and solid rejects in addition to material loss during loading and unloading activities. Pollution in Sundarban is mainly caused by discharge of burnt oil and grease from mechanized boats
There is no direct influence of industries along the coast of West Bengal. But, at about 20 nautical miles upstream, an industrial complex at Haldia on the west bank of Hugli river, makes significant contribution to coastal pollution. In addition to that, the Hugli river carries discharge from a large number of industries located upstream (62 large and medium in West Bengal). It is reported that around 22 MLD of industrial wastewater is discharged into coastal waters in West Bengal.
Tourism related wastes
The tourist resort with respect to major pollution source is the Digha region and to a minor degree the Bakkhali (Fraserganj) area. There are about 400 hotels, holiday homes, some eating joints and sweetmeat shops in Digha. And only a few (about 10) such facilities are present in Bakkhali area. Other tourist areas within the Sundarban area include Sajnekhali, Pakhiralay, etc. Though there is no inventory available, the wastes generated from these resources are also directly discharged into the coastal waters. Water sample analysis from coastal sea of Digha Sankarpur area clearly shows considerable amount of biological pollution especially near New Digha and Digha beach. The coliform counts are also significantly high especially in the New Digha and Digha.
A portion of agricultural waste in the form of fertilizers, pesticides and insecticides also constitute an unaccounted pollution load, which drain ultimately into the coastal waters through creeks and rivers. It is reported that in 2003-2004, the total fertilizer use in the state was around 1261450 tonnes. Consumption of pesticides in the period 2002-2003 was around 3000 tonnes per year. Assuming that 1% of this fertilizer and pesticide use ends up as runoff in the water bodies, the annual fertilizer load in the coastal water would be around 5213 tonnes per year of nitrogen, 2574 tonnes per year of phosphorus and 4815 tonnes per year of potassium. While the pollution load for pesticides would be 4 kg/day of organic chlorine and 32 kg/day of organic phophorus.