Creosote has been used since the 1920s to preserve railroad ties and utility poles. It decays into a polycyclic aromatic hydrocarbon (PAH) that bioaccumulates in marine life, affecting the growth, reproduction and survival of aquatic animals. Creosote can also be released into soil and contaminate groundwater, where it can take years to break down.
Chromated copper arsenate
Chromated copper arsenate (CCA) is impregnated into timber and other wood as a preservative. Containing compounds of chromium, copper and arsenic, it has been banned for residential use in the US since 2003. The European Union issued a complete banin 2006. When treated wood decays in a landfill, copper, chromium and arsenic are released and leach into the water table. Both arsenic and chromium are classified as human carcinogens.
Pentachlorophenol (PCP) has been used as an herbicide, antimicrobial agent and disinfectant. The manufacture of PCP produces several contaminants, including dioxins that do not degrade. It is ubiquitous in the environment and in humans, where it accumulates in tissue, even those with no direct exposure. Researchers estimate 96.5% of PCP will end up in our soil, where it contaminates the food chain. In 1987, the EPA restricted all uses of PCP other than as a preservative for utility poles and railroad ties.
2-4-D and 2-4-5-T
The insecticide DDT and herbicides 2-4-D and 2-4-5-T are ingredients of Agent Orange. They also contain dioxin, one of the most toxic substances in existence, a carcinogen that leaches into groundwater. 4-D is still in use, but 2-4-5T was banned in 1985 after toxicologists concluded it was a persistent toxin and concluded that soil levels in excess of 1 part per billion (ppb) might constitute a health risk to humans. Prior to the 70s, concentrations used were 30-50 ppm, a magnitude thousands of times greater than the recommended limit.