Assessment of pesticide and heavy metal residues in tilapia fish from Machakos and Kiambu counties, Kenya
Abstract
Exposure to pesticides, heavy metals and other chemical residues cause harmful effects; they can
cause injury to human health as well as to the environment. Humans take up these chemicals
through skin absorption, respiration and ingestion of contaminated food. Among all foods, fish is
one of the main sources of chemical contaminants although fish products account only for about
10% of diet or less. The present study was conducted in Kiambu and Machakos counties with
objectives of determining the concentration levels of pesticides and heavy metals in edible parts
of fish from inland fish farms, The dietary intake of pesticide and heavy metal was also
estimated and compared with acceptable daily intakes of the World Health Organization (WHO)
guidelines so as to assess their potential health hazard.
A total of two hundred and thirty tilapia fish samples (n= 230) were collected from Kiambu and
Machakos counties in the months of September and October 2011. Following wet digestion, the
levels of lead and cadmium were determined in muscle, liver, gonad and brain of tilapia fish
using Atomic Absorption Spectrophotometer (AAS) fitted with cadmium and lead lamps set at
their respective wavelengths. To evaluate organochlorine concentration, fish samples were
extracted, cleaned and analyzed using Gas Liquid Chromatography (GLC) fitted with Electron
Capture Detector (ECD).
The data was subjected to descriptive statistics and Analysis of Variance (ANOVA) to test levels
of significance at 95% confidence limit using Statistical Analysis Software (SAS) 9.0 version.
Significance was noted at P< 0.005.
In Kiambu county, mean lead levels (x ± s.d) in brain, liver, gonad and muscle were 31.31 ±
28.27, 17.33 ± 20.64, 16.62 ± 15.42 and 3.78 ± 2.22 ppm respectively against `the benchmark
value of 0.5ppm.The average cadmium levels (x ± s.d) in the brain, liver, gonad and muscle
were 7.25± 6.59, 5.35 ± 6.12, 3.35 ± 4.16 and 1.66 ± 2.48 ppm respectively against the
benchmark level of 0.05ppm.However, only positive samples were considered. Out of the total
number of samples analyzed, only 40% were positive for lead and cadmium in Kiambu county
and 34 % in Machakos County.
In Machakos county, mean lead levels (x ± s.d) in the brain, liver, gonad and muscle were
30.40±20.56, 7.88 ±7.25, 13.29±14.28 and 12.22±22.96 ppm respectively against the benchmark
level of 0.5ppm.The average cadmium levels (x ± s.d) were 3.91±5.84, 2.90±3.58, 1.25±1.38 and
1.12±1.13ppm respectively against the benchmark level of 0.05ppm.
The Organochlorines exhibiting the highest concentration (x ± s.d) were o,p ‘-DDT with a mean
of 2.098±4.097 μg Kg-1 followed by p’p-DDD 1.684±3.666 μg Kg-1 in the brain tissues. This
was followed by p’p-DDD in muscle at 0.916±1.287 μg Kg-1 and pp-DDT at 0.916±1.916 μg
Kg-1. Machakos County had p,p’-DDT at a concentration of 0.158 μg Kg-1 ,p,p’-DDD had 0.097 μg
Kg-1 and p’-DDT had a concentration of 0.016±0.016 .
Statistically, there was no significant difference in the tissues analyzed for the concentration of
Pb in the two counties since pr/t/>0.05. Cadmium concentration in the gonad had a significant
difference between Kiambu and Machakos County since pr/t/=0.05.The brain, liver and muscle
did not show any significant difference in the concentration of Cadmium between the two
counties since pr/t/ >0.05 .
The results of the current study indicate the presence of relatively high levels of lead and
cadmium above permissible limits in fish from the study areas and recommend controlling
industrial and agriculture effluents into surface water and proper sitting of ponds to minimize
the risk of contamination of farmed fish by pesticides and heavy metal. However it was noted
that the number of samples that were positive with regard to the presence of all residues was
small compared to the total number of samples analyzed.
Citation
Masters in Pharmacology and ToxicologyPublisher
University of Nairobi Department of Public Health, Pharmacology and Toxicology