CHAPTER ONE
INTRODUCTION
The need to feed the world’s increasing population has prompted the use of agrochemicals to increase food production and ensure the continuation of the human race. Such agrochemicals include pesticides like 2, 4-diphenoxyacetic acid, (2, 4-D), several formulations of inorganic fertilizer and the subject of this study Roundup. The increased use of pesticides in agricultural soils causes the contamination of the soil with toxic chemicals. When pesticides are applied, the possibilities exist that these pesticides may exert certain effects on non-target organisms, including soil microorganisms (Simon-Sylvestre and Fournier, 1979; Wardle and Parkinson, 1990). The microbial biomass plays an important role in the soil ecosystem where they play a crucial role in nutrient cycling and decomposition (De-Lorenzo et al., 2001). During the past four decades, a large number of herbicides have been introduced as pre and post-emergent weed killers in many countries of the world. In Nigeria, herbicides have since effectively been used to control weeds in agricultural systems (Adenikinju and Folarin, 1976). As farmers continue to realize the usefulness of herbicides, larger quantities are applied to the soil. However, the fate of these compounds in the soils is becoming increasingly important since they could be leached; in which case groundwater is contaminated or becomes immobile, and may persists on the top soil (Ayansinaet al., 2003). These herbicides could then accumulate to toxic levels in the soil and become harmful to microorganisms, plant, wild life and man (Amakiri, 1982).
Contamination of soil from pesticide mixing, loading, storage and rinsing at agricultural chemical dealership is a concern due to potential contamination of surface water and groundwater (Moormannet al., 1998). There is an increasing concern that herbicides not only affect the target organisms (weeds) but also the microbial communities present in soils, and these non-target effects may reduce the performance of important soil functions. These important soil functions include organic matter degradation, nitrogen cycle and methane oxidation (Hutsch, 2001). Roundup is the clear herbicide of choice for most illiterate farmers; it is used either alone or in combination with other herbicide preparations like 2, 4-Diphenoxyacetic acid apparently to achieve additive or synergistic action. It is mostly used in the rice farm to control post emergence weed. These farmers indulge in the use of Roundup and other herbicides to clear their farms prior to cultivation without cognizance to the obvious ecotoxicological impacts of such practices. The extensive use of Roundup and other herbicides by these farmers is attributable to the aggressive marketing strategies of the representative of the manufacturers in Nigeria who are able to demonstrate to these farmers the wonders their products could achieve, promising them less toiling on their farms with much better results. This is preached without commensurate caveat on the possible toxicity of these chemicals, and highlighting the possible danger of these chemicals to man and his environment
1.1Pesticide toxicology
Pesticide is the umbrella term for chemicals or biological used to control pests. The Environmental Protection Agency (EPA) defines a pesticide as any substance or mixture of substances/chemicals intended to prevent, destroy, repel or mitigate any pest (US-EPA, 2006). A pesticide need not always kill a pestː it could sterilize, or repel pests. Pests can be insects, mice and other animals, unwanted plants (weeds), fungi or microorganisms like bacteria and viruses. Pesticides can be classified in various ways such as, by their target, chemical nature, physical state and mode of action (Ware, 2000). Classification based on the target is perhaps the most widely known as the following examples indicate; Pesticides used to manage insects are called insecticides; and those used to manage rodents are called rodenticide; those used to manage fungi are called fungicides (Ware and Whitacre, 2004). Pesticides also include plant growth regulators, defoliants, or desiccants otherwise known as herbicide, the presence of a xenobiotic in the environment always represents a risk for living organisms. However, to talk about impregnation there is a need to detect the toxin in the organism, and the concept of intoxication is related to specific organ alterations and clinical symptoms. Moreover, the relationship between the toxic levels within the organism and the toxic response is rather complex and has a difficult forecast since it depends on several factors, namely toxicokinetic and genetic factors. One of the methods to quantify the exposure to xenobiotics and its potential impact on living organisms, including the human being, is the monitoring by the use of biomarkers.
