Aquatic systems under threat

T. NANDAKUMAR, THIRUVANANTHAPURAM, November 23, 2013

Heavy metal contamination endangering marine, inland fishes

Heavy metal contamination is emerging as a major threat to aquatic systems across the State, endangering both marine and inland fishes and posing a human health hazard.

Studies conducted by researchers in various colleges in Kerala have confirmed the presence of heavy metals in aquatic organisms in rivers and estuaries in the State.

Photo courtesy: The Hindu

A study by S.R. Lalsha and Jude Emmanuel of the PG Department of Environmental Sciences, St. John’s College, Anchal, revealed dangerously high accumulation of metals such as lead, zinc, and copper. The study covered five marine (Indian scad, Threadfin bream, Indian oil sardine, Indian mackerel and Mackerel tuna) and four inland fish species (Pearl Spot, Catla, Rohu and Red tailed barb), with samples collected from different markets in Thiruvananthapuram and Kollam and the Kallada river. The level of heavy metals in marine and inland species was found to be higher than the permissible limit recommended by WHO.

High accumulation of toxic arsenic was detected in all the marine species except Indian mackerel. Toxic cadmium was present in the muscles of all but one species, while highly toxic mercury accumulation was observed in the Threadfin bream (Killimeen). About 28.2 of the total lead reported in all the five marine species was accumulated in the muscles.

Metal burden

Among inland fishes, the level of toxic lead was found to be high. Cadmium was reported only in the liver of one inland species ( Catla catla ). All the fishes accumulated zinc, copper and lead. Among the tissues, the gills accumulated 49.83 per cent of the total metal burden followed by the liver (40.38). The concentration of lead was found to be high in the liver and muscles.

Fishes are capable of accumulating heavy metals in their living cells to concentrations much higher than those present in water, sediment, and microflora. Even essential metals such as copper, cobalt, zinc, iron, and manganese become toxic at high concentration.

Health hazards

Accumulated heavy metals enter the human metabolism through consumption of fish and may cause serious health hazards by disrupting the function of vital organs such as the heart, kidneys, liver, and bones. They also displace vital nutritional minerals, thereby hindering their biological function. The paper presented at the international conference on ecosystem conservation, climate change, and sustainable development here earlier this month says the detection of heavy metal accumulation necessitated regular monitoring of fish resources. The researchers said the study had confirmed the liver and gills of fishes as a reliable bio-monitor of heavy metal pollution.

Another study by P. Nimisha and S. Sheeba of the Department of Zoology, SN College, Kollam, detected high level of cadmium, copper, lead, zinc, and chromium in water samples collected from 60 km along the lower reaches of the Periyar river. The concentration of all the heavy metals in water was above the permissible limit. Relatively higher concentration of lead and zinc was observed.

A third study by C. Mini Chandran and P. Natarajan of the Department of Zoology, D.B. College, Sasthamcotta, showed high level of heavy metals such as copper, nickel, lead, and iron in the sediment samples collected from the Poonthura estuary in Thiruvananthapuram. The entire estuary was found polluted with lead, with the highest contamination at the bar mouth.