Biocide from antifouling paints affecting marine life,research says

“Surfaces immersed in aquatic environments are colonised by various organisms. Such colonisation and growth of organisms on surfaces is known as biofouling. Biofouling is an economic concern as it enhances friction on the hull of ship thereby increasing fuel consumption,impairing heat transfer efficiency of heat condenser tubes in power plants and may increase corrosion of metals and alloys,” explains DR N B Bhosale,emeritus scientist at NIO .

A team of 12 NIO researchers were involved in this study that lasted almost a decade. Extensive survey was carried out to establish the level of TBT contamination in Indian aquatic environment. Water,sediment and aquatic animals were collected from Maharashtra,Goa,Karnataka,Kerala,Gujarat,Tamil Nadu,Orissa and West Bengal. To study the TBT concentration in edible seafood,samples of fishes,oysters,mussels,squids,shrimps,crabs,solar shrimps and clams were studied from west coast of India. Globally,several million dollars have been spent annually to control biofouling on structures of economic importance. One of the commonly used methods to control fouling on ships is the application of paints containing toxic biocides. The biocide is slowly released into water,which does not allow the settlement of fouling organisms on the hull thereby,reducing the fouling.

However,TBT can diffuse from antifouling paints into surrounding waters where non-target organisms get exposed to this biocide. It is known that TBT is highly toxic to non-target organisms. For example,TBT at very low concentration (<10 nanogram/L) is acutely toxic to larvae of amphipods,lobster,crabs,shrimp,mussel,copepods,oyster,phytoplanktons and many other organisms. “Besides,TBT and its derivatives (DBT and MBT) are used as stabilisers in PVC industry,industrial catalyst,as bactericide and fungicide in timber industry. TBT is introduced into aquatic system by ship trafficking,ship scrapping and repair or as industrial effluents or waste,” Bhosale said. It is said that TBT is the most toxic compounds ever introduced by man in aquatic environments. TBT causes larval mortiltiy,reduced reproduction in lower invertebrates,imposex (Female turns into male) in gastropods,shell deformation and growth retardation in oysters due to its endocrine disrupting properties. Oyster fishery in Archon bay,France,was completely destroyed due to TBT pollution. Similar effects were seen in UK wherein,dogwhelk population had drastically decreased due to imposex. Due to catastrophic effects of TBT,it has been banned in several developed countries but it is still used in countries like India. The study was carried out to identify the level of TBT contamination in Indian aquatic environment.