Effects of Some Heavy Metals in Nigerian Food Products

Fish are widely acceptable in global menus due to their palatability, low cholesterol levels, tender flesh and ability to provide both a high source of animal protein and essential nutrients to the human diet¹. The occurrence of heavy metals in the environment may be caused by natural processes or by contamination resulting from human activities².

Heavy metals refer to metallic chemical elements that have relatively high density that is greater than water. Some heavy metals are toxic to humans, including arsenic, lead, aluminum, mercury and cadmium, while others (trace elements) are part of enzymes, hormones and cells in the body, e.g., iron, iodine, copper, zinc, chromium, selenium, fluorine and manganese³.

Fish have been reported as exceptional indicators for heavy metal contamination in aquatic and marine environments because they occupy different levels of the food chain⁴. In the human body, heavy metals such as lead have been reported to cause learning disabilities and impaired protein and hemoglobin synthesis, whereas cadmium has been reported as a cause of renal failure and calcium loss is responsible for malfunctioning in the peripheral and central nervous systems⁵.

Nigeria imports marine water fish as frozen fish, while freshwater fish are harvested from rivers, streams and fish ponds. There is presently an increase in the production and consumption of fish products in Nigeria due to the awareness of the potential health benefits. Therefore, a new study was conducted to evaluate the heavy metal concentrations of these fishes to compare the levels within and between them in order to ascertain the potential health impacts caused by their consumption⁶.

The study identified the presence of a wide range of heavy metals in fish samples consumed in Southeast part of Nigeria. All fish products had heavy metal concentrations below the permissible limits, except for the heavy metals of chromium and mercury. However, only mercury had a target hazard quotient>1.0; therefore, the consumption of fish products has the potential to cause adverse health impacts in humans.

The heavy metal concentrations for all fish samples did not show a consistent pattern. Arsenic was not detected in the freshwater fish samples. Fatal ingestion of cadmium could result in shock and acute renal failure and can occur from ingestion levels exceeding 350 mg g–1.

Chromium was observed in varying concentrations in some fish samples. The result of the current study showed that the level of cobalt in fish did not pose any health risks. Lead was detected in all the samples. Manganese was detected in all samples at levels below the permissible limit. Consuming the sampled fish products has the potential to cause adverse health impacts if not controlled.

Further studies are required to ascertain the source of mercury contamination in the freshwater fish samples. Different regulatory agencies are urged to conduct periodic heavy metal assessments to avert possible adverse public health hazards.

Keywords:

Heavy metals, fish, fresh and marine water, health risk, Nigeria, public health hazards, mercury contamination, regulatory agencies, heavy metal assessments, varying concentrations, hazard quotient>1.0.

References:

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