Identification And Concentration Of Selected Pesticide Residues In Ghanaian Cocoa Beans
Date
2017-07
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Publisher
University of Ghana
Abstract
Pest and disease have been the major causes of low cocoa production worldwide and the use of chemicals in the form of pesticides is one of the main ways of mitigating their undesirable outcome. However, inappropriate application of pesticides does not only affect the quality of cocoa bean products and the wellbeing of consumers of such products but can also damage the natural flora and fauna in the environment. Hence the reason why evaluating the concentrations of pesticide residues is necessary in establishing the quality of a cocoa. The goal of this study was therefore to determine the concentrations and distribution of specific pesticide residues in cocoa beans from the six cocoa growing regions of Ghana.
Three classes of pesticides were tested for in cocoa beans obtained from seventeen (17) districts in the Brong Ahafo, Eastern, Central, Western North, Ashanti and Western South cocoa growing regions of Ghana. These were the neonicotinoids (Thiamethoxam, Clothianidin, Imidacloprid and Acetamiprid); the synthetic pyrethroids (Cypermethrin, Deltamethrin, Fenvalerate, Lambda Cyhalothrin and Permethrin) and the organophosphorous compound Chlorpyrifos. Pesticide residue analyses were done separately on the whole unshelled beans, the nibs and the shells using a GC/ECD for the synthetic pyrethroids and organophosphorous compound and a QqQ-LC/MS for the neonicotinoids.
The results obtained showed that the mean concentrations of the neonicotinoids in all the three matrices ranged from <0.001 to 0.018 mg/kg in the shells, <0.001 to 0.0025 mg/kg in the nibs and <0.001 to 0.005 mg/kg in the whole beans with Imidacloprid being the predominant one. Ashanti Region had the highest concentration of Imidacloprid in all the three matrices whilst Eastern Region recorded the least concentration of Imidacloprid in the shells (0.009 mg/kg) and whole unshelled beans (0.002 mg/kg). In relations to the synthetic pyrethroids tested for, the results obtained indicated that out of the three matrices, it was only the shells that had recordable concentrations of pyrethroids being present and these were Cypermethrin (0.013 mg/kg) and Permethrin (0.012 mg/kg). Regional analysis also showed Permethrin to be present in bean shells from both Ashanti and Western South Region at concentrations of 0.01 mg/kg and 0.02 mg/kg respectively. Cypermethrin on the other hand was present in bean shells from four regions ranging in concentrations of 0.011 mg/kg to 0.020 mg/kg.
Chlorpyrifos which was the only organophosphorous compound tested for was found to be present in about 42% of the cocoa shell samples analysed at concentrations ranging from 0.0108 to 0.0396 mg/kg with an average concentration of 0.0184 mg/kg being recorded. Eastern Region had the highest concentration of Chlorpyrifos in the shells (0.026 mg/kg), while Western North Region recorded the highest concentration in the whole beans (0.027 mg/kg) and Central Region recorded the highest concentration in the nibs (0.015 mg/kg). On the whole, all the pesticide residue concentrations measured were below the established EU and Japan MRLs.
Principal Component Analysis (PCA) used to assess the associations amongst the various pesticides and between the pesticides and the regions revealed that Imidacloprid/Thiamethoxam; Thiamethoxam/Cypermethrin and Chlorpyrifos/Imidacloprid were in comparable proportions and prevalence in the cocoa nibs. For the shells however, Imidacloprid/Cypermethrin and Deltamethrin/Permethrin/Thiamethoxam were of similar proportions. PCA of the whole cocoa beans also indicated a close association between Cypermethrin/Thiamethoxam and Permethrin/Clothianidin. Out of all the regions, Central Region had the highest association with all the 10 pesticides in the shells and with Imidacloprid in the whole beans whilst Western South Region showed an association with Chlorpyrifos in the nibs.
Description
Thesis (MPhil)
Keywords
Identification, Concentration, Pesticide Residues, Ghanaian Cocoa Beans, Ghana