to their extensive use and handling of jet fuel, lubricants and other chemicals. Chemical spills can be mitigated or prevented by spill containment structures and clean-up equipment such as vacuum trucks, portable berms and absorbents. Deicing fluids used in cold weather can pollute water, as most of them fall to the ground and surface runoff can carry them to nearby streams, rivers or coastal waters. Deicing fluids are based on ethylene glycol or propylene glycol. Airports use pavement deicers on paved surfaces including runways and taxiways, which may contain potassium acetate, glycol compounds, sodium acetate, urea or other chemicals. During degradation in surface waters, ethylene and propylene glycol exert high levels of biochemical oxygen demand, consuming oxygen needed by aquatic life. Microbial populations decomposing propylene glycol consume large quantities of dissolved oxygen (DO) in the water column. Fish, macroinvertebrates and other aquatic organisms need sufficient dissolved oxygen levels in surface waters. Low oxygen concentrations reduce usable aquatic habitat because organisms die if they cannot move to areas with sufficient oxygen levels. Bottom feeder populations can be reduced or eliminated by low DO levels, changing a community's species profile or altering critical food-web interactions. Glycol-based deicing fluids are toxic to humans and other mammals. Research into non-toxic alternative deicing fluids is ongoing. Air pollution Aviation is the main human source of ozone, a respiratory health hazard, causing an estimated 6,800 premature deaths per year. Aircraft engines emit ultrafine particles (UFPs) in and near airports, as does ground support equipment. During takeoff, 3 to 50 × 1015 particles were measured per kg of fuel burned, while significant differences are observed depending on the engine. Other estimates include 4 to 200 × 1015 particles for 0.1–0.7 gram, or 14 to 710 × 1015 particles, or 0.1–10 × 1015 black carbon particles for 0.046–0.941 g. In the United States, 167,000 piston aircraft engines, representing three-quarters of private airplanes, burn Avgas, releasing lead into the air. The Environmental Protection Agency estimated this released 34,000 tons of lead into the atmosphere between 1970 and 2007. The Federal Aviation Administration recognizes inhaled or ingested lead leads to adverse effects on the nervous system, red blood cells, and cardiovascular and immune systems. Lead exposure in infants and young children may contribute to behavioral and learning problems and lower IQ. Mitigation Aviation's environmental footprint can be mitigated by reducing air travel, optimizing flight routes, capping emissions, restricting short-distance flights,