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1. First, chemical pesticides are often not just toxic to the organisms for which they
were intended, but also to other organisms. Chemical pesticides can be subdivided into
two groups: non-selective and selective pesticides. The non-selective products are the
most harmful, because they kill all kinds of organisms, including harmless and useful
species. For example, there are herbicides that kill both broad-leaf weeds and grasses.
This means they are non-selective since they kill nearly all vegetation.
2. Another disadvantage of chemical pesticides is resistance. Pesticides are often
effective for only a (short) period on a particular organism. Organisms can become
immune to a substance, so they no longer have an effect. These organisms mutate and
become resistant. This means that other pesticides need to be used to control them.
3. A third drawback is accumulation. If sprayed plants are eaten by an organism, and
that organism is then eaten by another, the chemicals can be passed up the food
chain. Animals at the top of the food chain, usually predators or humans, have a
greater chance of toxicity due to the build-up of pesticides in their system.
4. The last and most significant threat relates to the remains or residues of pesticides
which are left behind on the crops. Residue may be consumed on fruit or vegetables,
for example, and for this reason crops may not be sprayed close to harvesting.
Alternatively, the remains of pesticides may soak into the soil or groundwater and the
contaminated water might then be used to spray the crops or be drunk by animals.
NatalieR answered the question on May 23, 2022 at 07:54
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