ABSTRACT
The study investigated the levels of organochlorine pesticide residues in both cocoa beans and soils of cocoa plantations in selected farms in Ondo State. Soil samples and cocoa pods were collected from four major farms in the State. The pesticide residues were extracted, cleaned up and analysed using Gas Chromatography-Electron Capture Detector (GC-ECD). In the analysed cocoa samples, the ranges of the mean concentrations of the organochlorine pesticides were: α-HCH (ND-0.094 mg/kg), β-HCH (ND-0.371 mg/kg), γ-HCH (ND-0.032 mg/kg), δ-HCH (ND-0.032 mg/kg), heptachlor (ND-0.272 mg/kg), heptachlor-epoxide (0.040-0.185 mg/kg), aldrin (ND-0.117 mg/kg), dieldrin (0.052-1.110 mg/kg), endrin (0.297-1.516 mg/kg), endosulfan I (1.719-10.689 mg/kg), endosulfan II (0.028-0.570 mg/kg), endosulfan sulphate (ND-3.865 mg/kg), p,p’ DDT (ND-0.100 mg/kg), cis-permethrin (0.078-0.662 mg/kg), trans-permethrin (0.085-0.927 mg/kg). However, the levels of aldrin, dieldrin, endrin and endosulfan in the cocoa samples analysed were found to be high and above Maximum Residual Limits (MRLs) established by WHO/FAO (HCH isomers, heptachlor, heptachlor-epoxide, aldrin, endrin and dieldrin (0.020 mg/kg) and endosulfan I, II and sulphate (0.100 mg/kg)) and European Union (α-HCH, β-HCH and δ-HCH isomers, heptachlor, heptachlor-epoxide, and dieldrin (0.020 mg/kg), γ-HCH (1.000 mg/kg), p,p’-DDT, aldrin (0.050 mg/kg) and endosulfan I, II, cis- and trans-permethrin (0.100 mg/kg)) . In the soil samples analysed, the ranges of the mean concentrations of the organochlorine pesticides were: α-HCH (ND-0.064 mg/kg), heptachlor-epoxide (0.059-1.384 mg/kg), aldrin (ND-0.450 mg/kg), dieldrin (0.041-0.066 mg/kg), endrin (0.136-0.567 mg/kg), endosulfan I (0.319-1.451 mg/kg), endosulfan II (0.033-0.113 mg/kg), endosulfan sulphate (0.764-1.711 mg/kg), cis-permethrin (0.077-0.259 mg/kg), trans-permethrin (0.079-0.151 mg/kg) The mean concentration of aldrin, dieldrin, endrin, endosulfan (I and II) in the soil sample analysed were above the MRLs of the analytes established by Netherlands aldrin(0.0025mg/kg),dieldrin(0.0005mg/kg),endrin(0.001mg/kg),endosulfanI(0.050mg/kg),endosulfanII(0.050mg/kg). p, p’ DDT was below detection limit (10-4 mg/kg) in 50% of the analysed cocoa and all the soil samples. Similarly, HCH isomers and p,p’ DDT were below detection limit (10-4 mg/kg) in the soil samples analysed except Oluji-1 where α-HCH was detected. The results of the bioaccumulation factors showed that endosulfan, dieldrin, endrin heptachlor, heptachlor-epoxide, cis- and trans-permethrin were bioaccumulated in the cocoa samples from the selected farms. The high bioaccumulation factors of endosulfan I (7.367 in Oluji-1, 3.084 in Oluji-2 and 14.525 in idanre), Dieldrin (27.073 in Oluji-2, 7.477 in Owena), and cis- and trans-permethrin (1.8 and 11.734 in Owena, 8.597 and 8.429 in Idanre respectively) give cause for concern considering the adverse health hazards pose by high accumulation of these pesticides on man. This indicated recent use of these pesticides despite the ban imposed on their use. The results of ANOVA showed that there was no significant difference between the mean concentrations of the pesticide residues in all the cocoa samples (p<0.05). Similarly, no significant difference was observed between the mean concentrations of the analytes in all the soil (p<0.05).
CHAPTER ONE
1.0 INTRODUCTION
Cocoa is an important tropical tree crop which does not only provide farmers with much desired income to meet their basic family needs1 but also serves as aforeign exchange earner for many West African countries like Nigeria, Ghana, Côte d’Ivoire, Cameroon and Togo.Its botanical name, Theobroma Cacao, given by Swedish natural scientist Carl Von Linne denotes its rich taste and high nutritional value which make it irresistible to both young and adult especially when processed into diverse products such as chocolate, sweet, cocoa drink, cocoa biscuit, cocoa bread, cocoa cake, cocoa flakes, cocoa popcorn, cocoa jam, cocoa jelly, cocoa cream, cocoa wine and spirit, etc.2-4
Cocoa was believed to have originated in the hot, humid region near the source of the River Amazon in South Africa and introduced into Nigeria in 1874.1,5In Nigeria, Cocoa is grown mostly in Southern States such as Ondo, Oyo, Ogun and Osun. It is a tropical lowland crop which flourishes best where the annual rainfall is at least 1140mm with mean temperature below 170C. It requires shade to reduce moisture evaporation especially at the nursery and the early stages of its establishment in the field. It also requires a deep, fertile and well aerated loamy soil which must beloose and friable. The cocoa plant when mature reaches a height of 7.5 to 10.5m.6
Before 1960, exportation of cocoa accounted mainly for the agricultural export, which made over 80% of the Gross National Product (GNP) of the Nigerian economy.7This showed that cocoa was the chief source of foreign exchange earnings for Nigeria before the discovery and exploration of crude oil. Despite the oil boom experienced in Nigeria, cocoa still serves as the major agricultural export crop and accounted for about 38% of agricultural export in 1997.8Being an important agricultural produce, cocoa provides employment for the farmers in the remote villages and millions of individuals all over the world involved in its processing, marketing and distribution. It is imperative to note that large scale production of cocoa can solve the problems of unemployment in Nigeria. This is because the world demand for cocoa and its derived products is ever increasing and remains insatiable. Eighty-five percent (85%) of the cocoa demand of the European Nations is from West Africa where Nigeria is one of the major exporters5. This showed that the final destination of West African cocoa is Europe.
Although, the cocoa producing Nations in West Africa derive revenue from the export of cocoa to Europe, much more revenue could be derived if the exported cocoa is being processed within the West African region and the finished products is exported for the consumption of the European nations after the satisfaction of the local demands. This could only be achieved if laws are enacted and necessary provisions are made to provide a very conducive environment for the farmers and the local processing industries to strive.However, the discovery of abundant natural resources, such as crude oil in Nigeria, gold in Ghana, probably led to the reduction in effort of most African Governments to make available these required provisions. Consequently, cocoa farming is now left mostly to smallholder farmers (with farm size less than 5 hectares) who rely on the crop as the primary source of income.8 Many of these farmers are geographically isolated, illiterate, poorly informed and have very limited resources for proper crop management. This development has caused a sharp decline in cocoa production as many of the farmers still adopt the traditional methods of farming which is very inefficient and pose high risk to the farmers8.
Unfortunately, the enormous effort of these farmers at sustaining production under high risk conditions was not most often reflected in their output as pests and diseases largely contributed to decline in cocoa production.9In Nigeria, decline in cocoa production started in 1971 and 1972 with yield of 255,000 and 241,000 metric tonnes respectively5. The lowest yield in the 70’s was recorded in 1978 with output of 137,000 metric tonnes5. Yields declined further from a peak of about 350,000 metric tonnes in the mid 80’s to about 58,700 metric tonnes in 19865. According to THISDAYLIVE Newspaper report issued on 21st January, 2014, the cocoa production in Nigeria was 250, 000 metric tonnes in 2011, 300, 000 metric tonnes in 2012, and 350, 000 metric tonnes in 2013. This showed an annual increase in production by 50, 000 metric tonnes but when compared to the annual cocoa production from other West African countries in the same period (Ghana cocoa production was between 850, 000 – 1, 000, 000 metric tonne per annual and Cote d’Ivoire cocoa production was in the range 1.2 – 1.4 million metric tonnes per annual), it would be obvious that the growth rate was not only insignificant but also the annual output was too small for the most populated black Nation (Nigeria) that is expected to champion the course of self sustenance in food production in Africa.
Major contributors to this decline were pests as 25-30% loss in yield of cocoa was attributed to the cocoa mired, Sahlbergella singularis while about 17% was lost through the feeding of the cocoa pod borer Characoma strictigrapta10, 11. The collective efforts of minor pests (such as the shield bug, Bathycoelia thalassina, the pod miner, Mamara species, the root-feeding termites, Macrotermes bellicosus,Mesohomotoma tessmanniand the cacao thrips, Selenothrips rubrocinctus)could become significant especially under suitable conditions in young cocoa or ageing cocoa plantations.
It is important to note that several concerted research efforts have been made to develop various control techniques (such as cultural, biological and chemical) which could be adopted for integrated management of the major and minor pests of cocoa in Nigeria. It is however quite unfortunate to note that many of the findings of such research hardly reached the local farmers and when they did eventually, the inability of the farmers to read and write often hindered the proper interpretation of those findings. Despite the various mechanisms developed for pest management, the farmers rely greatly on the use of pesticides (chemical control technique) because it provides immediate and quicker remedy in the periods of serious pest outbreaks.11
There are over seven hundred (700) chemicals in use as pesticides, which are formulated into about thirty-five thousand products classified as insecticides, herbicides, fungicides and rodenticides.12Although, pesticides are known to be very efficient in pest control, reliance and prolonged application of thesesynthetic chemicals had given rise to numerous problems which affected the food chain and posed negative impact on biological diversity. It has been established that pesticides application could lead to serious health hazard ( such as epilepsy, stroke, respiratory disorders, leukemia, convulsion, brain and liver tumors ) and environmental pollution as it is often manifested in the disturbance of the ecosystem,which include destruction of some natural vegetation, pollution of the important water bodies (ground water, river water, drinking water), soil and air as well as reduction and extinction of some aquatic species and wildlife population.13-15
