Effects of pesticide residues on the growth and yield of vegetables at Navrongo of Ghana

Abstract

BackgroundThe constant use of pesticides on farmlands is a source of food poison and potential cause of disease to humans in most parts of Africa. The lack of in-depth knowledge on the choices of use of the pesticides and their applications by most farmers in our African communities is a key to unsafe food and unhealthy living. Furthermore, the impact of some of these pesticides on the growth and yield of vegetable crops is largely unexplored. The present research was conducted in the Tono Irrigation Dam area of Navrongo, Ghana, where vegetable cultivation holds substantial economic importance making it a critical aspect of the local economy. In this study, we identified prevalent pesticides used in Navrongo’s vegetable cultivation, quantified pesticide residues present in selected vegetables grown, and assessed the impact of the pesticides on the vegetable crops’ growth and yields.MethodsThirty vegetable farmers at the Tono Irrigation Dam Area, Navrongo were randomly selected, and interviewed face to face. Questionnaires were also employed for data acquisition. Vegetables were sampled by dividing the farmland of each of the vegetable types in to three equal portions, and from each of the three portions, one sample was collected which was then put together with the other two samples as one. The samples were packed in zip-lock bags and kept at a cold temperature (− 20 ℃) before being transferred to the laboratory where they were thawed, homogenized and then subjected to extraction. The extract obtained was subjected to a clean-up process and then analyzed on a GC–MS instrument for pesticide detection and quantification.ResultsThe interview revealed number of years of farmers’ engagemrent in vegetable cultivation from one to ten, and identified four key vegetable varieties grown by the farmers: Capsicum annuum (pepper), Abelmoschus esculentus (okra), Solanum aethiopicum (garden egg) and Solanum lycopersicum (tomato). The data acquired gave identities or names of eight pesticides that are applied on the cultivated vegetables or farmlands by the farmers, and a decision on the vegetables selected for analysis in this study. Furthermore, the study revealed dichlorodiphenyltrichloroethane (DDT), k-optimal, lindane, and lambda-cyhalothrin to be among the pesticides in use, with DDT being a non-degradable, and the most widely applied pesticide. Notably, the DDT, lindane, and hexachlorocyclohexane, residues exceeded safety limits set by the European Commission in pepper, garden egg and okra. Unfortunately, banned pesticides such as heptachlor and aldrin were detected in the cultivated vegetables. More alarmingly, the commonly used DDT and lambda-cyhalothrin in the vegetable cultivation were found to hinder seed germination and seedling vigor in an investigation.ConclusionsThe DDT, lindane, and hexachlorocyclohexane, residues detected in the pepper, garden egg and okra samples that exceeded safety limits render these vegetables unsafe for human consumption. The banned heptachlor and aldrin detected in the vegetables indicate long-lasting environmental contamination. The commonly used DDT and lambda-cyhalothrin in the vegetable cultivation found to hinder seed germination and seedling vigor, indicate their non-degradability and substantial growth impediments. This present study therefore underscores the urgent need for enhanced safety measures and informs pesticide practices to safeguard both crops and public health in the district. We recommend further research be conducted to assess the potential health implications associated with the cultivation and consumption of vegetables in Navrongo, Ghana.