"Excessive use of chemicals such as insecticides and pesticides causes a threat to ecology." Explain with reason.

(N/A) $(i)$ Excessive use of fertilizers and pesticides, when washed away by rain or irrigation, causes water pollution.
$(ii)$ These chemicals can be toxic to many non-target plant and animal species, leading to a loss of biodiversity and environmental pollution.
$(iii)$ Runoff containing high levels of nutrients from fertilizers may lead to eutrophication in water bodies, causing oxygen depletion.
$(iv)$ These chemicals often accumulate in the food chain, resulting in biological magnification, which poses severe health risks to higher trophic levels, including humans.