Legacy pollutant is a collective term used to describe substances whose use has been banned or severely restricted by the U.S. EPA. Because of their slow rate of decomposition, these substances often remain at elevated levels in the environment for many years after their widespread use has ended. No additional loading of legacy pollutants is allowed or expected due to EPA restrictions. Gradual declines in environmental legacy pollutant concentrations occurs as a result of natural attenuation processes.
Tarrant County water bodies on the State 303d list due to concentrations of legacy pollutants in fish tissue that have resulted in the issuance of a fish consumption ban by TDH.
Chlordane was introduced in 1948, and was used extensively as a broad spectrum insecticide to control soil insects on agricultural crops, as a home lawn and garden insecticide, as a fumigating agent, and for termite control . EPA suspended the use of chlordane on food crops in 1978, and phased out other above ground uses over the following five years. All uses except underground application for termite control were banned in 1983. Manufacture and sales were halted in 1987, and use of existing stores was allowed until April 1998 when sale and use were terminated.
Source Analysis continued.
DDT was initially used in WWII for control of disease carrying insects, and was used extensively as a broad spectrum insecticide for the control of almost all agricultural and disease-carrying insects. It was used extensively in the 1950s and 1960s for mosquito control in urban areas. DDD is a metabolite of DDT and was itself manufactured as a pesticide for several years. Most uses of DDT, and all uses of DDD, were banned by EPA in December 1972. DDE is the major degradation product of DDT and DDD, and is among the most widely occurring pesticide residues.
Source Analysis - continued
Dieldrin was used as a pesticide, and is a degradation product of the pesticide aldrin. Although aldrin was used in greater quantity, it is rapidly converted to the more persistent dieldrin in the environment. Both pesticides were used primarily for the control of rootworm and cutworm with some use in the citrus industry and for mosquito larvae and termite control. All food crop uses of both compounds were canceled in May 1975, and only subsurface injection for termite control was allowed after that time. All remaining uses were cancelled in 1987.
Source Analysis – continued.
PCBs are a group of synthetic organic chemicals containing 209 possible individual compounds, which vary in chemical and physical properties, toxicity, environmental persistence., and degree of bioaccumulation. PCBs were manufactured as mixtures of different congeners, and generally sold under the name Aroclor. PCBs were most widely used as coolants and lubricants in transformers, capacitors, and other electrical equipment. In 1976 TOSCA banned, with limited exception, the manufacture, processing distribution in commerce, and use for PCBs. TSCA also required the EPA to promulgate regulations for proper use, cleanup, and disposal. TSCA and subsequent EPA rules did not require PCB-containing materials to be removed from service and many are still in use (EPA, 1999). A substantial portion of PCBs manufactured before 1977 still remain in service, although these are being phased out as equipment is replaced or decontaminated.