lesions, they healed over time by itself. inhalation effects hccpd is highly toxic to animals when inhaling its vapours. no human studies regarding lethality were done, but there has been an incident involving a waste water treatment centre where humans were exposed, from which most relevant human information is taken. human inhalation effects there is data for human exposure to hccpd for numerous organ systems. waste water treatment plant and water cleanup crew workers were exposed after industrial release of the compound into the environment. the initial concentration of the compound in air was unknown but was later determined to be ranging between 0.27 and 0.97 ppm. workers noticed a strange odor on the plant and even a blue haze after a heavy rain. when some of them sought medical attention, it was determined the plant was contaminated with hccpd, and numerous tests were performed to document these circumstances. approximately one fifth of waste water treatment workers reported having nausea and abdominal cramps after exposure for a period between 3 and 15 days. they also reported respiratory complaints like sore throats, coughing and breathing difficulty. however, tests on lung function and chest x-rays did not show any abnormalities. workers exposed to hccpd for a longer time reported respiratory irritation, nasal irritation and sinus congestion, most likely because of direct contact of these tissues with hccpd from the air, and not as a systemic effect through the lungs. in addition, elevated levels of lactic dehydrogenase was found in 11 out of 41 workers from the wastewater treatment. these levels was not nearly as high for workers from the water cleanup crew, but the aspartate aminotransferase levels were elevated for 12 out of 97 of these workers. these enzymes might indicate damage to heart, as well as to the liver. no evidence of heart function impairment was found in both worker groups though. the elevated levels in patients diminished after a period of 3 weeks. animal inhalation effects for prolonged exposure, significant differences occur between lab animal species. where all mice died in the first week in a 13-week study, being exposed to 2 ppm hccpd for 5 days a week, 6 hours a day, rats however survived until the third week. for a very low exposure of 0.04 ppm, 3 out of 20 mice died and none of the rats died. chronic exposure of hccpd at very low concentrations produced a yellow-brown pigment in the lung, tracheal and nasal epithelium in rats and mice. the pigmentation did not disappear after the exposure stopped. for acute high exposures (1 hour, 42 ppm) all animals died, after showing difficulty breathing and gasping for air. their lung tissues showed hemorrhagic lesions, inflammation, edema and necrosis in the bronchi. however recovery of the animals that survived was apparent 2 weeks after the treatment. cardiac and gastrointestinal function seemed not be impaired after exposure of hccpd in rats, mice and monkeys. moderate hepatic tissue degeneration was observed for acute inhalation. the same tissue degeneration was observed for longer experiments with lower concentrations. history hccpd is a highly toxic organochlorine compound that was first mentioned as a diene in certain diels-alder reactions in 1930. the hccpd chemical family quickly attracted increased attention with the discovery of its insecticidal properties in 1955 and extensive commercialization. however, due to extensive use, the hccpd family of insecticides (chlordane, aldrin, dieldrin, endrin, heptachlor) became less effective as a result of genetic mutations of the targeted insects. the number of insects resistant to cyclodienes and lindane approached 300 by 1989. later, in 1957, another use of the compound was found, namely as a flame retardant for polyesters. in addition, hccpd was used to make a dimer. this dimer was also known as “mirex” or “box dimer” and was offered commercially as a flame retardant to be used in polymers such as polypropylene. in the 1970s, it was shown that the mirex dimer degrades in the environment into kepone, a well established carcinogen. this development raised concern and the use of mirex was completely discontinued. before this, diels-alder adducts of hccpd were developed with a number of cyclic dienes. some of these compounds gained commercial attention such as the adduct of hccpd with 1,5-cyclooctadiene, which was sold under the name dechlorane® plus. this flame retardant was used in polyolefins and nylon and also in wires and cables, due to its good moisture resistance. in the meantime, scientific research has also demonstrated its impact on the environment today, almost all hccpd derivatives have been banned or are under consideration for banning, according to the deliberations of the stockholm convention on persistent organic pollutants. however, given that hccpd is a versatile raw material for the synthesis of a wide range of end products, as of october 2021 it is still available commercially.