Aquatic Pollution and Coastal Management

Unit 4 : Pesticide pollution

4.15.How Organisms might be affected by a Pollutant

Morphology

• Experiments on Pleuronectes sp.showed that at 0.18 ppm of copper for a month resulted in the replacement of mucus cells by chloride cells, this indicated that the production of chloride cells might be to excrete copper ions and thus explains acclimatization.
• Low levels of zinc were found to cause the vertebral damage in fish. This clearly indicates that, effect, like this are disadvantageous to the fish in natural environment. The experiments carried out in the College of Fisheries, Mangalore have clearly indicated the damage of vertebral column of fingerlings of common carp exposed to low levels of cadmium.
• Secretion of byssus threads in mussels have been used to assess water quality. The mussels are found to get rid of the extra load of metals through the secretion of byssus threads.
• Sea urchin eggs are sensitive. They go on accumulating heavy metals till critical concentration, which inhibits the enzyme system responsible for protein synthesis, cell migration, cell division etc., thus producing abnormal larvae.

Physiology

• Many species of fish exposed to low levels of heavy metals for a longer period have shown stunted growth in the experiments conducted in the laboratory. The fish presumably spends more energy to detoxify the metals which results in less energy available for the growth of the individual. Further, the rate of food intake also was found to be one of the causes for poor growth efficiency in the experimental fish.
• Exchange of CO₂ for O₂ in the body is a good indicator for sub-lethal assessment. The experiment requires good clinical equipment to measure the O₂ tension in small samples of blood.
• When fish is exposed to low levels of metals, it tries to clear off its gills by increasing the coughing frequency. This can be measured by implanting a tube in the buccal cavity and with attachment to for transducer and pressure records. Apart from the above parameters, monitoring of heart beat and blood pressure are used to study the sub-lethal effects on fish exposed to low levels of toxicants.

Reproduction
Hydroids exposed to low levels of heavy metals exhibited lower rates of a sexual reproduction ultimately causing total deformities in the colon. The long term impact of sublethal concentration of a pollutant on fish population,whether capable of reproducing successfully or not in the environment is crucial.
Reproductive failure may be due to:

• Direct toxicity results in reduced fertility.
• May not complete life cycle.
• May not go to breeding ground.

Behaviour
Experimental works have shown that heavy metals can impair processes such as settlement, feeding and swimming activity.Inhibition of feeding in fishes exposed to low levels of toxicants for a longer period has observed. Fishes may not return to their original habitat after spawning when they were exposed to low levels of toxicants.

Biochemistry
There is a relation to the levels of pollutant and haemotocrite. Usually erythrocyte sedimentation rate, and red and white blood cell counts are used during sublethal studies. In addition, histochemical studies are used to recognize the damages caused at sub -cellular levels in different organs.

Genetics
Chromosome make-up abnormalities in the early embryonic stages are perhaps the most sensitive practical indicators of the sublethal effects of aquatic pollutants on reproduction in fish. Experiments have shown aberrations in the giant chromosomes of chiranomid larvae exposed to low levels of toxicants.