Synthetic fertilizer contains phosphorous, which creates algae in ponds and lakes, that can kill fish by removing the oxygen from the water. Phosphates and nitrates, which are components of synthetic fertilizer, contaminate water, rendering it undrinkable. And a byproduct of synthetic fertilizer, oxidized nitrogen, increases smog in the air. This can cause respiratory illness and more asthma in children and adults who ordinarily do not have these issues, plus aggravating respiratory problems in people who already suffer with them.
With the air already polluted by car emissions, factory gasses, and burning coal, synthetic fertilizer adds insult to injury. It significantly increases the risk of emphysema and other serious, and sometimes fatal, respiratory illnesses. One need never smoke anymore to get lung cancer these days. One need only go outside and take a deep breath.
More and more people are abandoning synthetic fertilizer and going organic. Collecting compost, using mown grass cuttings, and natural manure, grow far healthier plants and do not pose a risk to your health.