In July 1976, an accident occurred at the Industrie Chimiche Meda Societa Azionaria (ICMESA) chemical plant near Seveso, Italy, and 2,3,7,8-tetrachlorodibenzo-/»-dioxin (TCDD) was released into the environment. The Seveso accident was caused by a runaway exothermic process in a trichlorophenol (TCP) batch reactor. The high temperatures led to a synthesis of TCDD, which was subsequently released into the atmosphere through a vent designed to relieve excessive pressure buildup in the reactor. The explosion released a toxic vapor cloud containing 1500 kg of various chemicals and upto a possible 30 kg of TCDD. The atmospheric deposition of the TCDD contaminated a total area of 18 km2, with levels in the most contaminated area around the factory reaching 20mgm~2. Impacts on human health were of primary concern, with much of the literature regarding this incident being related to human health issues. Ecological damage caused by the Seveso accident is considered below.
After the Seveso accident, thousands of small domestic animals died within a few weeks. Animal mortality and pathology had been observed after the accident and TCDD tissue levels found in animals from the Seveso area had been reported. At the time of the accident, more than 80 000 domestic animals, mainly rabbits and poultry, were present in areas that were subsequently contaminated. Most of the domestic animals were fed on fodder harvested close to or around the farm. The deaths started some days after the incident and increased markedly within the first 2 weeks, then decreasing in subsequent months. Massive mortality was observed among rabbits with 32% dying in the most contaminated zone, and 8.8% and 6.8% mortality was observed in the intermediate- and low-contaminated areas, respectively. A higher mortality was noted on the farms where animals were fed fodder obtained from the contaminated area. TCDD soil levels in the most-, intermediate-, and less-contaminated areas were up to 5477, 44, and 5 p,gm~2, respectively. Shortly after the accident, autopsies were performed on domestic animals from farms of the Seveso area, and TCDD tissue levels were determined for them. Of the 309 rabbits analyzed from the TCDD-contaminated area, 203 were TCDD-positive. Ninety-seven percent of the analyzed rabbits were positive with a range from 3.7 to 633 ng TCDD g~ liver and a mean of 84.9 ng TCDD g~ liver in the most-contaminated area. Autopsies showed various pathological signs such as hepatic lesions and hemorrhage.
The most-contaminated area was artificially reconstructed and transformed into a wood composed mainly of oaks with some scattered green fields and some bushy areas, the Bosco delle Querce urban park. The fauna of the Bosco delle Querce in comparison with 11 other urban and suburban parks in the Lombardy region have been analyzed. According to the analyses, a 4-year monitoring survey revealed that the present ecological and biological index of the park shows full ecological recovery as an urban park. Biocoenosis is well composed, and colonization of annelids, insects, amphibians, reptiles, birds, and mammals has occurred. The results of an action study of xenoestrogen-like molecules (i.e., gametogenesis and the gross morphology of genital organs in rabbits and house mice) show no signs of TCDD effects. The TCDD levels in liver of the animals from the Seveso park and controls were found to be 4.3 ± 0.4 and 7.2 ± 2.9 pg g~ fat for rabbits, and 29.5 ± 13.8 and 41.3 ± 9.5 pgg-1 fat for mice, respectively. The contamination levels found in the Seveso park suggested that the TCDD biological risk in the Seveso park does not differ significantly from that in the other parks investigated. This shows that, for small to medium metropolitan areas, good environmental policies would help in ecological recovery of the terrestrial environment, even in heavily chemically contaminated areas.
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