Metals, hydrocarbons, and other toxic chemicals are more specific to urban runoff. Indus-trial discharges have been strictly regulated over the last 20 years, and most of the worst problems have been cleaned up. Now the everyday actions of individuals contribute a greater share of urban runoff pollution. Vehicles are probably the single worst offenders. Because brake pads and tires wear directly onto roads, the metals and other contaminants that they deposit are transported very efficiently to the stormwater system.
Vehicles are also the leading source of hydrocarbons in urban runoff.
Oil and other automotive fluids are constantly leaking onto roads and parking lots. In fact, urban gardeners use up to 10 times more toxic chemicals per acre than farmers. Harm to aquatic life Not surprisingly, the cumulative effects of urbanization are devastating to aquatic life. Sedimentation, pollutants, high storm flows, low summer flows, and high temperatures all take their toll. Numerous studies have shown that after urban development fish and macroinvertebrate communities alike decrease in total numbers, become less diverse, and are composed of more pollution-tolerant species.