Heavy metals and pesticide residues as quality determinants for sustainable management of prawns along the Indian coastline of Tanzania

Abstract

The presence of heavy metals and pesticide residues in prawns, water and sediments, were determine. Prawns, sediments and water samples were collected along prawns fishing zones in the Indian coastline of Tanzania. Zinc (Zn), lead (Pb) and cadmium (Cd) were analyzed using Atomic Absorption Spectrophotometry (AAS). Direct Mercury Analyzer (DMA) was used for mercury (Hg) analysis. Pesticide residues were analyzed by Gas ChromatographyMass Spectrophotometry

(GC-MS). Information on stakeholder’s perception on the sources of aquatic pollution was collected using a structured questionnaire. Results indicated that, fertilizer (60.7%), pesticides (59.8%) and herbicides (60.7%) were the main sources of aquatic pollution. Cyberdip and Utupa-mixed local herbs were the chemicals used in prawns fishing. Heavy metal contaminants were predominant in sediments followed by prawns, and water. The heavy metals were highly concentrated in prawns and sediments in the order of Zn > Pb > Cd > Hg, and Pb > Zn > Cd > Hg in water respectively. Lambda-cyhalothrin was the only pesticide residue detected in prawns and sediments but not in water. Lambdacyhalothrin levels detected in prawns from Kisiju and Kilwa were 5.6 – 45.2 folds above the

maximum acceptable limits. Lambda-cyhalothrin levels in sediments was 175; 4070 and 4432 folds higher than the maximum acceptable level in Bagamoyo, Kilwa and Kisiju respectively.

Presence

of Zn, Pb and lambda-cyhalothrin beyond acceptable limits in prawns and sediments may indicate marine pollution. The maximum acceptable level of lambdacyhalothrin

in sediments is 0.00372 mg/kg and the maximum acceptable level of lambdacyhalothrin

for prawns is 0.05 mg/kg. These pollutants may impair quality and safety of prawns and by-products which is a risk to the public health. Therefore, monitoring of agricultural and the anthropogenic activities around prawn fishing areas is inevitable.