Ecology: The Biology of Interaction. VI-10. The Pesticide Problem

VI-10. The Pesticide Problem
In the breast milk of nursing mothers in the United States, DDT content is 4 times higher than allowed by sanitary standards for cow's milk. In the United States, this is commented upon as follows: «If mother's milk were in different packaging, it would not be allowed to be sold at all»
V. Eichler, 1993
The development of agriculture over recent decades is closely linked to the use of an increasing quantity of pesticides («toxic chemicals»).
«The application of broad-spectrum pesticides can lead to pest «resurgence», i.e., their appearance after treatment in greater numbers than before. This is because the preparation kills both pests and the predators that controlled them. A good example of this kind is the use of DDT to combat caterpillars of the small white (Pieris rapae), or simply cabbage white, that parasitizes Brussels sprouts. Initially, DDT treatment produced a noticeable effect, but gradually the number of pests became even higher than on the control (unsprayed) plots. The difference was even more pronounced with repeated applications of DDT to «suppress» new population outbreaks of the pest. Analysis of the agroecosystem showed that the pesticide concentration in the leaves eaten by caterpillars rapidly decreases due to the overall growth of the green parts of the cabbage. However, the level of the toxic chemical in the soil remains high, especially if plant residues are plowed in after harvest. As a result, caterpillars hatching from eggs laid on leaves after treatment suffer weakly, while the numbers of their main enemies — ground beetles (Harpalus rufipes) and harvestmen (Phalosium opilio) — decline. Suffering less from predators, pests substantially increase their chances for survival, which is not compensated even by the toxic chemical. Its further application only worsens the situation»
(Material from Wikipedia – the free encyclopedia, 2007).
To the above, it should be added that, since «pests» become animal species that reproduce rapidly, for many of them the emergence of resistance to the pesticides used is recorded, with subsequent wide spread of resistant forms. This problem is solved by transitioning to the use of new, more effective pesticides. In general, it can be said that pesticide application initially leads to a yield increase, followed by its decline.
One of the dangerous characteristics of pesticides (like many other pollutants) is their ability to concentrate during transfer along trophic chains. This effect was particularly well studied on the example of DDT (dichlorodiphenyltrichloroethane), the first pesticide to achieve wide distribution. The insecticidal properties of DDT were discovered in 1938 (the Nobel Prize was awarded for this discovery). After World War II, DDT became almost a panacea for all troubles related to insects. The almost complete eradication of lice in developed countries is a result of its use. Unfortunately, negative consequences of its use began to be discovered later.
DDT and products of its decomposition are capable of accumulating in fatty tissues. Thus, during the investigation of one water body, the following DDT concentration values were recorded (in ppm — weight parts per million): water — 0.00005; plankton — 0.04; fish — from 0.2 to 2 (predatory); heron — 3.5; osprey egg — 6; cormorant — 26 (Odum, 1975). As can be seen, during the transition to higher trophic levels, concentration (biological amplification) of the pollutant occurs in the biomass. Accumulation of DDT in the eggs of large birds leads to calcium metabolism disruption and increased fragility of the eggshell. Spread of DDT along trophic chains led to its contamination of the entire biosphere. For example, it caused eggshell damage in penguins in Antarctica, where it was never applied.
As a result of clarifying the pathways of DDT transfer and its accumulation in organisms, the production and use of this substance was banned. Experts note that DDT is not more dangerous than other pesticides that continue to be used. DDT simply was not «lucky» — it became the first pesticide whose harmfulness was well studied.
In general, it can be said that pesticide application leads to such unfavorable consequences:
— development of resistance in pests;
— pest resurgence and secondary population outbreaks;
— increased costs for food production;
— destruction of natural regulators of pest numbers;
— unfavorable impact on the environment and human health.
A partial solution to the pesticide problem is the use of non-persistent pesticides that rapidly degrade in the natural environment. A complete solution is the use of biological control measures against «pests», including:
— use of natural enemies;
— use of crops resistant to attack by phytophagous insects;
— release of artificially sterilized males (such males mate with «wild» females, which as a result do not leave offspring);
— agrotechnical control methods (changing environmental parameters: sanitary-hygienic measures, changing agricultural techniques, crop rotation, polyculture, customs control, etc.);
— Use of natural compounds that affect «pests» — hormones, attractants, etc.
Pesticide is a rather broad concept, meaning any substance used to destroy pests or weeds. Pesticides include insecticides, bactericides, fungicides, acaricides, zoocides (targeted at rodents), nematicides (directed against mollusks), herbicides (means against weeds). Some of the most common categories of pesticides are:
— Organophosphorus compounds (OPs): chlorophos, carbophos, methylnitrophos, avin, methylacetophos, etc. Neurotoxic poisons. Mild poisoning — headache, sweating, lethargy, insomnia. Further — fear, depression, damage to digestive and respiratory organs. Chronic poisoning — toxic neurasthenia, vegetative-vascular dystonia. Frequent psychic damage — irritability, memory impairment, intellectual decline.
— Organochlorine compounds: DDT, HCH (hexachlorocyclohexane), heptachlor, chlordane-polychloropinene, polychlorocamphene, chlorobenzene. Highly persistent, fat-soluble, capable of accumulating in organisms (in lipid media, from which they do not pass into water). The most powerful channel of elimination (and contamination) — through breast milk. The most sensitive are nervous tissue and cardiac muscle. Chronic poisoning — headache, dizziness, tingling in extremities, liver pain, digestive disorders.
— Organomercurial compounds: granosan, mercur, mercurhexan. Purpose — seed dressing. Poisoning is possible when grain is stolen. With birds that eat grain and fish from water bodies where water from fields flows, mercury in the form of methylmercury spreads through ecosystems. They cause various metabolic disorders. Chronic poisoning: emotional instability, headache, dizziness, memory impairment, insomnia, fatigue, sweating, hand finger trembling.
— Carbamates: seviram, tiram, cyram, cyneb — products of carbamic acid and its derivatives. Not very toxic, similar in action to OPs, carcinogenic, have a very broad spectrum of action.
— Nitrophenolic compounds: nitrophen, dinitrophen — products of processing coal tar phenols. Acute poisoning — «heat stroke» syndrome, chronic — euphoria, drowsiness, headache, sweating, dermatoses.
— Copper-containing preparations: copper sulfate, Cuprum sulfate, Bordeaux mixture, copper oxychloride, copper trichlorophenolate. Fungicides and seed dressing. Damage to gastrointestinal tract, respiratory organs, dermatitis.
Some other toxicants, although not belonging to pesticides, ecologically prove to be quite similar to them. These include such substances:
— Nitrates (nitrites) — in food, they are most often the result of excessive or incorrect application of fertilizers to soils. Nitrites bind with oxyhemoglobin, forming methemoglobin. The lethal dose is from 3.5 g of sodium nitrate. Chronic poisonings manifest as lethargy and depression; in large doses, nitrites damage kidneys, liver, CNS, gastrointestinal tract.
— Lead (Plumbum). The main source — tetraethyllead, which is used to increase the octane number of gasoline, printing equipment, radiation protection (much Plumbum was dispersed after the Chernobyl accident). Easily absorbed as dust. Deposited in tissues, especially in bones. Protoplasmic toxin. Increases brain excitability. Early symptoms — dark stripes on front teeth. Later — lead encephalopathy.
— Other heavy metals: Mercury, Zinc, Manganese, Chromium, Nickel, Cadmium, etc.