Generally, the environment becoming increasingly contaminated with heavy metals. Ultimately, they get deposited in aquatic environment where most of the waste products are eliminated.
by L.H.D.Hansamali & J.M.N.J.Jayathilake
Accumulation of heavy metals inside the human body is a recent topic to the field of health in Sri Lanka. Number of studies have recorded low level of heavy metals in the blood stream of randomly selected individuals in some areas of the island. But, the source and magnitude of exposures are still assessing by researchers and suggesting suitable public health interventions. However, the definite source of heavy metal intake of some people of Sri Lanka is still unknown.
Generally, the environment becoming increasingly contaminated with heavy metals. Ultimately, they get deposited in aquatic environment where most of the waste products are eliminated. The major risk of this scenario is accumulating heavy metals in living fish tissues. Majority of them are getting accumulated in liver, kidney and gills and rarely in fish muscles, comparing to the other tissues.
However, the metal concentration in muscle tissue is important because it is the common and edible portion of fish that plays an important role in human nutrition, has been reported to have the lowest concentration of metals except for cadmium compared to other heavy metals. Findings show that fish species contained higher concentration of metals in liver and lower in flesh and the concentrations of the metals in the organs are in the order of liver > gills > flesh.
Apparently, the per capita fish consumption is estimated around 31.4 kg/year in Sri Lanka. The number is increasing yearly with the awareness of its nutritional and therapeutic benefits. The consumption of fish contaminated with heavy metals tend to accumulate these metals in human body resulting severe health hazards. The heavy metals most commonly associated with poisoning of humans are lead, mercury, arsenic and cadmium.
Lead is an environmental contaminant that can cause serious damage to human health. Young children are vulnerable to toxic effects of lead and can suffer profound and permanent adverse health effects, particularly the development of brain and nervous system. Lead also causes long-term harm in adults, including increased risks of high blood pressure, kidney damage, and neurological effects.
Compounds containing cadmium are also carcinogenic. Ingestion of any significant amount of cadmium causes immediate poisoning and damage to liver and kidneys. Excessive Cd exposure may give rise to renal, pulmonary, hepatic, skeletal, reproductive toxicity effects and cancer. There may be behavioural and neurological changes associated with overexposure to mercury poisoning, such as excitability and quick-tempered behaviour, lack of concentration, and loss of memory. Neurological symptoms include brain damage, nerve disease of the extremities, pericapillary haemorrhages within the white matter, and loss or deficiency of the fatty coverings around these nerve fibres. Skin problems include transverse white bands on the fingernails and excessive accumulation of fluid in the soft layers of tissue below the skin.
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| Figure: The process of accumulation of heavy metals through food fish |
Though there are many ways in ingestion of heavy metals, accumulation through food fish is one of most possible ways worldwide. Therefore, many international monitoring programs have been established in order to assess the quality of fish for human consumption and to monitor the health of the aquatic ecosystem. Further, the industries that dispose wastage with heavy metals should implement proper methods to prevent this emerging global threat.
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