Increased pollution of air and aquatic environment by natural and anthropogenic activities has led to biosorption of heavy metals by aquatic plants and animals in the habitats. The absorbed heavy metals pose a health hazard to both aquatic inhabitants such as Penaeus indicus and their consumers. Contamination due to heavy metal consumption by such aquatic plants and animals were presumed to affect their tissuelar qualities which are consumed as food.
Recent studies on concentrations of Mn, Cu, Zn, Pb and Cd in whole prawn specimens and water samples from Epe Lagoon, Lagos State, using Techcomp AA 6000 atomic absorption spectrophotometer yielded concentrations of the order of Mn; 69.36 ± 78.53mg/kg > Zn; 52.88 ± 4.01mg/kg > Cu; 54.82 ± 13.88mg/kg > Pb; 9.18 ± 7.18mg/kg > Cd; 0.83 ± 0.20mg/kg with the mean concentrations of Mn, Cu and Pb in prawn specimens being above the maximum limits recommended by World Health Organisation.
This study therefore considered the effect of heavy metals on tissue mechanics of African prawns, P. indicus at Mnarani Old Ferry location in Indian Ocean, Kenya. Ten litres of water and 0.5kg soil sediments samples were obtained from six sites of Indian Ocean along the Mnarani Old ferry mixed and sediment ground for homogeneity, analyzed using the XRF for presence of heavy metals, then used in aquaculture for the test experiment.
The control experiment was done using water and soil sediments from heavy metal free sites. The presence of Iron (Fe), thallium (Tl), lead (Pb) and nickel (Ni) was established in the homogeneous water and soil sediment samples. Tissues from mature P. indicus from the test aquarium and control were ethically extracted and tested for heavy metals showing presence of Fe, Tl, Pb and Nickel in the tissues from test aquarium. The mechanical properties of P. indicus tissues were determined and compared experimentally in the laboratory.
The Young’s modulus for tensile properties for tissues with heavy metals was 256.72 kPa exceeding the measurement for tissues without heavy metals by 69.45 kPa. Tissues with heavy metals were found to be hard, stiff and with high strength when compared to tissues without heavy metals. The hardness, stiffness and strength for tissues with heavy metals were 2.70 kPa/mm2, 68.03 N/m, and 112.62 kPa exceeding the respective measurements for tissues without heavy metals by 1.40 kPa/mm2, 12.63 N/m, and 33.12 kPa.
It has been reported that heavy metals bond with tissue proteins altering their structure thus tissues become strong, stiff, hard and with higher young modulus due to heavy metals contamination. This study therefore informs environmentalists, health sector specialists, food scientists and standards controls about effect of heavy metal poisoning on the African prawns, P. indicus which compromises on their quality as food.
