Why would some environmentalists say that nitrogen fertilizers harm the environment twice?

Question

Why would some environmentalists say that nitrogen fertilizers harm the environment twice?

Answer 1

Nitrogenous fertilisers will give nitrates and it will be seeping into the groundwater. Excessive nitrates say more than 45mg/Liter will cause health problems. Infact Nitrates are the reason for blue baby disease.

Answer 2

Well, first they enter soil by seeping into the ground and then they percolate into the water table which takes the nitrogen into a water body. When nitrogen levels increase in the water, a algea bloom can occur which absorbs dissolved oxygen in the water. This afects normal plant and animal life within the water and can eventually cause death of aquatic species.