The negative impact of fertilizers comes from 3 major ways: The first is that because they are rich in phosphorus and nitrates thy boost algae production when they reach rivers and lakes. Second, they also impact in a negative way to the human if it is in contact with the water. Three it's production contributes to global warming.
Explanation:All right, fertilizers might seem a good resource. However hey stimulate the algae if they reach the water. Thus, when they grow more than they are expected to grow they just consume the oxygen underwater life has access to. Also, they provide a great number of nitrates to the water and if the human body is in contact with it, well there could be a grade of poisoning. Finally, when they are produced the process contributes in a very considerable way to the global warming effect.