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УДК 631.348.45:632.954
H. S. M. AL-DELFI, G. M. BELLO Х. Ш. М. АЛЬ-ДЕЛЬФИ, Г. М. БЕЛЛО PESTICIDES APPLICATION: THREAT TO ECOSYSTEMS ПРИМЕНЕНИЕ ПЕСТИЦИДОВ: УГРОЗА ЭКОСИСТЕМАМ
(Поступила в редакцию 08.04.14)
This paper reviewed the uses of pesticides such as for crop В статье исследуется использование пестицидов для
protection, preservation of food, prevention of vector-borne защиты растений, сохранения продуктов питания, профи-
diseases (like malaria) etc. It also further discusses how pesti- лактики трансмиссивных болезней (таких как малярия) и
cides application causes direct or indirect acute and chronic т.д. Предложены рекомендации по сокращению использо-
ecological damage to man animals. Based on the review, the вания пестицидов и использованию других альтернатив,
paper finally concluded by suggesting some recommendations поддержки научных исследований и интенсивных програм-
for pesticides users and government policy makers in Nigeria ма борьбы с вредителями сельскохозяйственных культур. such as; reduce reliance on pesticides and encourage use of other alternatives; strong science-based and research-supported and intensive IPM program is required amongst others.
Introduction
Pesticides have numerous beneficial effects. These include crop protection, preservation of food and materials and prevention of vector-borne diseases. For example pesticides may be used in the prevention of malaria, which kills up to 1 million children per year especially in the tropics, and for preventing other vector-borne diseases such as dengue, leishmaniasis and Japanese encephalitis. Pesticide use has resulted in acute and chronic ecological damage either by direct injury such as birds and fish or by indirect effects such as elimination of natural enemies; particularly long-lasting effects have included the depression or stimulation of reproduction in organisms.
Pesticides are toxic by design - they are BIOCIDES, designed to kill, reduce or repel insects, weeds, rodents, fungi or other organisms that can threaten public health and the economy. Their mode of action is by targeting systems or enzymes in the pests which may be identical or very similar to systems or enzymes in human beings and therefore, they pose risks to human health and the environment. Pesticides are ubiquitous in the environment and most are synthetic. There is growing concern about children's exposure to pesticides and their special susceptibility. Children are not little adults, and may have higher exposures and greater vulnerability at both high and low levels of exposure [14].
Insecticides are mostly used in developing countries and fungicides/herbicides in developed countries. Consumption increased substantially over time, for example, in the USA, the use of pesticides doubled from 1960 to 1980, but total use has since remained stable or fallen. Most pesticides are used in agriculture, but in 1999 about 74 % of households in USA were reported to use at least one pesticide in the home [1, 23].
Use has risen in developing countries and the fastest growing markets in Africa, Asia, South and Central America, Eastern Mediterranean. There is a high pesticide use on crops grown for export [22]. Although developing countries use only 25 % of the pesticides produced worldwide, they experience 99 % of the deaths. This is because use of pesticides tends to be more intense and unsafe, and regulatory, health and education systems are weaker in developing countries [8, 21].
Food production started from time immemorial, with the geometric increase in population of human beings the need to increase food production to feed large number of people led to the advent of technologies like machines, herbicides among others. New production technologies designed to revamp the agricultural sector and boost agricultural production has led to marked increase in crop yields. The issue of providing adequate food supply to meet requisite demand in Nigeria has been topical for a number of years, problems of food production and distribution has been elaborately analyzed with a variety of policy recommendations, among which is the use of agrochemicals not only to increase food production but to reduce food waste and hopefully enhance food producers income. The conventional methods of raising farm productivity since the World War II has centered on employing the use of externally acquired inputs like fertilizers and protection chemicals among others [2].
With the increasing awareness concerning health hazards associated with herbicides on the part of consumers, environment and farming groups, there has been a consequent demand for more stringent regulatory measures in the development of environmentally safe agrochemical formulations. However, mankind will still continue to use chemicals to produce adequate supplies of food and feeds, while trying to minimize associated risks to human health and the environment. Risk is an intrinsic part of life and must be weighed against the benefits likely to result from any particular action [2].
Nigeria government should adopt policies or strategies as it has been done in other countries including Australia, Canada, European Union countries, Japan, Norway, Switzerland and United States which instituted various forms of green payments, that is payment to farmers who adopt sustainable farming practices. Other policy options include taxes, removal of subsidies, a tax on fertilizers or pesticides, or removal of subsidies for these inputs would discourage excessive use [19].
Level of usage determines pesticides impact
In the 1940s manufacturers began to produce large amounts of synthetic herbicides and their use became widespread. Some sources consider the 1940s and 1950s to have been the start of the agrochemical era. According to [13], agrochemical use has increased 50 fold, since 1950 and 2.3 million tonnes (2.5 million short tonnes) of industrial pesticides are now used each year. Seventy-five percent (75 %) of all herbicides in the world are used in developed countries however; its use in developing countries is increasing. Many herbicides can be grouped into chemical families. Prominent pesticide families include organocholrines, organophosphates and carbamates. Organochlorine hydrocarbons (DDT) could be separated into dichlorodiphenylethanes, cyclodiene compounds, and other related compounds. Prominent families of herbicides include pheoxy and benzoic acid herbicides (2, 4-D) tyriazines (atrazine), Ureas (diuron), and Chloroacetanilides (alachlor). Many commonly used herbicides are not included in these families, including glyphosate.
Presently, there are about 1000 pesticide formulations in use throughout the world today; the listing of all hazards to ecosystems would be enormous, particularly with most individual pesticides having different effects on various species. Agriculture and forestry are the primary source of pesticides in ecosystems. Clearly delineating these effects is complicated by the fact that there are 5 10 million species in the environment. The United Nations offers a list of pesticides considered most hazardous to humans. While valuable, this list is limited, since it is restricted to acutely lethal doses in humans (based on studies in the rat and other laboratory species). In general, insecticides generally are the most toxic pesticides to the environment, followed by fungicides and herbicides. Exceptions exist for certain herbicides which are highly toxic, and are far more hazardous to the environment than are insecticides. The most hazardous pesticides include those that can be distinguished on the basis of either water or fat solubility. Water soluble compounds are easily transported out of the target area into ground water and streams; fat soluble chemicals are readily absorbed in insects, fish, and other animals, often resulting in extended persistence in food chains [27]. Some of the most troublesome pesticides to the ecology are (a) insecticides: DDT, dieldrin, diazinon, parathion, and aldicarb; (b) herbicides: 2-4-D, atrazine, paraquat, and glyphosate, and (c) fungicides: benomyl, captan, mercury, copper, and pentachlorophenol. About 5 million ton of pesticides are applied annually in the world, of which about 70 per cent is used for agriculture and the remainder by public health agencies and government agencies for vector control and by home owners. In many countries, agriculture and forestry occupy approximately 50 per cent of the land area. When croplands are treated, some impacts of pesticides occur on non-target terrestrial and aquatic ecosystems, as well as on adjoining agro ecosystems.
Forests are important wildlife habitats. Two broad classes of pesticides are used in forests: insecticides to control insect pests, and herbicides used to suppress the growth of shrubs during the regeneration process. Over the last thirty-five years, two large-scale pest control programmes have been used in forests of eastern Canada and of the north-eastern United States in attempts to control spruce budworm; from 1980 to 1983 in Czechoslovakia, similar programmes were initiated to control the larch bud moth. In the latter programme, a mixture of pyriphosmethyl and permethrin eliminated many invertebrate species, but recovery was relatively rapid [20]. In eastern Canadian forests, DDT caused fish mortality [10] as a result of bioaccumulation through the food chain [26]. Lethal and indirect effects of decreasing the biomass of insect food would be expected to affect insectivores, but that has rarely been demonstrated. Extensive mortality of canopy-dwelling song birds has been observed with applications of phosphamidon and to a lesser extent, with fenitrothion; ground-nesting birds and small mammals were unaffected [15]. Generally, the safety margin of OPs for canopy dwelling birds is small.
Pesticides application technologies
The past decades have witnessed a dramatic change in agriculture with food production soaring due to the Green Revolution. The Green Revolution entailed the use of improved technologies; particularly the breeding of high yielding food crop varieties, the expansion of irrigation, mechanization, specialization and the use of chemical fertilizers and pesticides. However, the Green Revolution has been criticized for its adverse human health and environmental impacts. For example, agricultural intensification through excessive and inappropriate use of chemical fertilizers and pesticides, has polluted water bodies and degraded soils, led to biodiversity loss by killing beneficial plants, insects and other wildlife and in some cases poisoned farm workers, to mention but just a few.
In pesticides application, one the sprayer's requirements is achieving coverage of crop plant surfaces with pesticides is part of the problem, as is placing the pesticides into the target area because it is known fact that generally, less than 0.1 per cent of all pesticides applied reach the target pests, according to some estimates. If so, then a large fraction of applied pesticides may be available to contaminate water, soil, and atmosphere and may disrupt non-target species.
Under ideal weather conditions, less than 25 per cent of the ULV-applied pesticide reaches the target. Likewise, most drifts often contaminate untreated terrestrial and aquatic ecosystems. Pesticides application with air blast sprayers, only about 65 per cent of the pesticide reaches the target area and whereas 35 per cent goes elsewhere. If ground boom sprayers are used about 70-80 percent of the sprayed pesticide would reach the target under the same weather normal conditions. Dusts (susceptible to drifts due to extremely low weight), chemigration (application of pesticides in irrigation water) and granules also pose major problems to non-target pests, particularly birds. Birds mistake the granules for gravel, and may consume them with disastrous results.
Clearly, the need exists to improve pesticide application technology to assure that more pesticide reaches the target points and to reduce hazards to human and ecosystem.
Impacts of pesticides on plants, animals and ecosystems
According to [13], agrochemical use has increased 50 fold, since 1950 and 2.3 million tonnes (2.5 million short tonnes) of industrial pesticides are now used each year. Seventy-five percent (75 %) of all herbicides in the world are used in developed countries however; its use in developing countries is increasing. The environmental impact of pesticides is often greater than what is intended by those who use them. Over 98 % of sprayed insecticides and 95 % of herbicides reach a destination other than their target species, including nontarget species, air, water, bottom sediments, and food [12].
The amount of pesticide that migrates from the intended application area is influenced by the particular chemical's properties: its propensity for binding to soil, its vapour pressure, its water solubility, and its resistance to being broken down over time [9]. According to [9], factors in the soil, such as its texture, its ability to retain water, and the amount of organic matter contained in it, also affect the amount of pesticide that will leave the area. Pesticides can contaminate unintended land and water when they are sprayed aerially or allowed to run off fields, or when they escape from production sites and storage tanks or are inappropriately discarded [18].
Pesticides impacts depend on level in the ecosystem. Ecosystems, whether plant or animal, can suffer from accrued damage to individuals. In plants, nitrogen fixation, which is required for the growth of higher plants, is hindered by pesticides in soil [17]. The insecticides DDT, methyl parathion, and especially pentachlorophenol have been shown to interfere with legume-rhizobium chemical signaling [17]. Reduction of these symbiotic chemical signaling results in reduced nitrogen fixation and thus reduced crop yields [17]. Root nodule formation in these plants saves the world economy $10 billion in synthetic nitrogen fertilizer every year [5].
Pesticides can kill bees and are strongly implicated in pollinator decline, the loss of species that pollinate plants, including through the mechanism of Colony Collapse Disorder [6]; [25]; [7] and [29] in which worker bees from a beehive or western honey bee colony abruptly disappear. Application of pesticides to crops that are in bloom can kill honeybees [3] which act as pollinators. The USDA and USFWS estimate that US farmers lose at least $200 million a year from reduced crop pollination because pesticides applied to fields eliminate about a fifth of honeybee colonies in the US and harm an additional 15 % [12]. On the other side, pesticides have some direct harmful effect on plant including poor root hair development, shoot yellowing and reduced plant growth [24]
Similarly, the effects of pesticides on animals (bird, aquatic life, amphibians and even human) inflict extremely widespread damage to biota, and many countries have acted to discourage pesticide usage through their biodiversity action plan. Animals may be poisoned by pesticide residues that remain on food after spraying, for example when wild animals enter sprayed fields or nearby areas shortly after spraying (Palmer, Bromley, and Brandenburg, 2007). Widespread application of pesticides can eliminate food sources that certain types of animals need, causing the animals to relocate, change their diet, or starve [3] Poisoning from pesticides can travel up the food chain; for example, birds can be harmed when they eat insects and worms that have consumed pesticides [3]. Earthworms digest organic matter and increase nutrient content in the top layer of soil. They aid in protecting human health by ingesting decomposing litter and serving as bioindicators in soil activity while creating a richer environment. A number of studies have shown that pesticides have had harmful effects on growth and reproduction on earthworms, which are in turn consumed by terrestrial vertebrates such as birds and small mammals [28]. Some pesticides can bioacumulate, or build up to toxic levels in the bodies of organisms that consume them over time, a phenomenon that impacts species high on the food chain especially hard [3].
In humans, farm workers and their families experience the greatest exposure to agricultural pesticides through direct contact with the chemicals which enter the human body through inhalation of aerosols, dust and vapor that contain pesticides; through oral exposure by consuming food and water; and through dermal exposure by direct contact of pesticides with skin [4] and prolong exposure to pesticides can range from mild skin irritation to birth defects, tumors, genetic changes, blood and nerve disorders, endocrine disruption, and even coma or death [11]. In Nigeria according to [16] the common health hazard associated with application of herbicides is fatigue, though people employed for application of herbicides read instruction label before its application, they do not observe other instructions like wearing of mask and the right direction during herbicides application.
Conclusion and recommendations
Both in the developed and developing countries there is injudicious and indiscriminate use of pesticides and presence of pesticide residues in food, fruits, vegetables and environment is a matter of grave-concerns. Banned and highly hazardous pesticides have been used without any precautionary measures. Exposure of farm families to pesticides and intake of pesticides by consumers are a major health threat. Biotic and abiotic systems have been affected entirely. Based on this review work the following recommendations have been drawn: reduce reliance on pesticides and encourage use of other alternatives; raise farmers' knowledge about pests, agro-ecosystem and the surrounding environment; encourage use of low risk pesticides in cases of inevitable pesticide use; conserve and use useful natural enemies and parasites to suppress crop pests; selection of appropriate pesticides and their handling and use as per the label are the most important steps for safe use of chemical pesticides. For this, the Government needs to develop mechanisms for enforcing the regulations for the overall management and use of pesticides, adopting FAO guidelines with adequate educational and training interventions; research and development on the use of biopesticides and eco-friendly measures are highly recommended to minimize the use of hazardous pesticides. For this, research laboratories must be strengthened in terms of both human resources and physical infrastructure; long-term implications of pesticide use on human health and environment need to be studied for sustainable agriculture, safety to human health and the environment as a whole.
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