Pesticides in Environmental Compartments of Afram Arm of the Volta Basin in Ghana
Date
2015-07
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Publisher
University Of Ghana
Abstract
Inappropriate use of agrochemicals, especially insecticides along the banks of the Afram River in Ghana raises food safety concerns as well as concerns of pollution of the aquatic ecosystem. These environmental compartments along the Afram arm of the Volta Lake are therefore investigated for pesticide residues. Levels of three groups of pesticides (organochlorines, synthetic pyrethroids and organophosphates) were analysed in farmland soils, watermelon, onion and chili pepper as well as some aquatic biota (fish species, and submerged macrophytes), water and surface sediment. In the case of aquatic fauna, pesticide content of three tissues: muscle, gill and liver of Tilapia zilli, Oreochromis
niloticus, Chrysichthys nigrodigitatus and Bagrus bayad were determined. Two aquatic macrophytes:
Ceratophyllum demersum and Nymphaea lotus were also analysed and bioconcentration factors for quantified pesticides evaluated. Presence of banned pesticides were investigated in the analysed matrices, health risk assessment of pesticide residues in the food commodities for systemic effects conducted, toxicity of sediment investigated and effect of periodic flooding of cultivated lands on pesticide content of water assessed. Approximately 97% of target pesticides analysed were detected and quantified in soil samples of fallow lands; 24% of which exceeded the maximum residue limit (MRL) of the United States Environmental Protection Agency (USEPA). About 88% of total soil samples analysed contained one or more pesticide residues. The Farmland soils temporary left to fallow were therefore found from this study to have high load of residual pesticides. The pesticides that exceeded the USEPA maximum residue limits
were p,p’-DDT, p,p’-DDD, fenvalerate, cypermethrin, permethrin, chlorpyrifos, dimethoate,
chlorfenvinphos and methamidophos; and the banned pesticides detected were: aldrin, dieldrin, endrin, gamma-lindane, DDT, heptachlor, parathion and methamidophos. Incidence rate of the pesticides in the food commodities was very high; 100% of target organophosphate and pyrethroids as well as 80% of the organochlorines were quantified in the food commodities (watermelon, onion and pepper samples)
analysed. While 38% of the quantified pesticide residues exceeded the European Union (EU) MRL, estimation of health risk associated with pesticide present in the food crops indicate that β-lindane,
dieldrin and methamidophos have potential for systemic toxicity in children while heptachlor shows health risk in both children and adults. Also, comparison of pesticides content of water during flood and recess regimes show significantly high incidence rate and concentration levels of pesticides, as well as high number of pesticides exceeding the WHO MRL during the flood regime. Determination of Afram
River bed sediment toxicity identifies γ-lindane, p,p’-DDE and dieldrin as contaminants whose concentration levels affect the integrity of the Afram arm of the Volta Lake ecosystem as a whole and pose health risk to benthic organisms in particular. The mean concentration range of pesticides in the four fish species was highest for organochlorines (0.78 μg/kg – 4671 μg/kg), followed by synthetic pyrethroids
(1.10 μg/kg – 49.8 μg/kg) and then the organophophates (1.60 – 17.00 μg/kg) while total pesticide load in the fishes follow the order: C. nigroditatus > B. Bayad > O. niloticus > T. zilli. Pesticide content was significantly higher (p ≤ 0.05) in liver than in gill and muscle tissues. The concentration order in the tissues was generally: Liver > Gill > Muscle. Whereas the levels of methoxychlor, aldrin, bifenthrin, permethrin, cyfluthrin, cypermethrin, chlorpyrifos, chlorfenvinphos, ethoprophos and profenofos in the muscle tissues of the fishes exceeded 0.01mg/kg default EU MRL, estimation of health risk indicates that levels of only heptachlor, α-endosulfan and ethoprohos in the fish species present health hazard in children (up to 11 years), while no health risk can directly be imputed or associated with adult consumption of these fishes. While Ceratophyllum demersum and Nymphaea lotus have been found to
bioconcentrate pesticides, Ceratophyllum demersum in particular was found to fulfill the “very
bioaccumulative” criterion since it was able to have bioconcentration factor of approximately 5000 for some pesticides like diazinon and fenitrothion in the aquatic medium. Interaction with the farmers indicates that most of them are well acquainted with the right application of agrochemicals but fail to do so. This attitude has resulted in high pesticide residue levels in various environmental matrices along the
Afram River bank of the Volta basin. Most of the farmers, either due to ignorance or deliberate refusal, do not observe the required Pre-harvest interval (PHI) that has the effect of reducing pesticide residues to acceptable levels in food crops before consumption. It is therefore necessary to put appropriate policy and legislative measures in place to ensure compliance to this important requirement that is particularly relevant in improving food security in fruit and vegetable cultivation.
Description
Thesis (PhD)
Keywords
Pesticides, Agrochemicals, Insecticides, Food Security, Ghana