Chronic community exposures

CHRONIC COMMUNITY EXPOSURE Hazardous Waste Sites... 

Where sufficient toxicologic information was available, MRLs were derived. MRLs are specific for route (inhalation or oral) and duration (acute, intermediate, or chronic) of exposure. Ideally, MRLs can be derived from all six exposure scenarios (e.g., Inhalation - acute, -intermediate, -chronic Oral - acute, -intermediate, - chronic). These MRLs are not meant to support regulatory action, but to acquaint health professionals with exposure levels at which adverse health effects are not expected to occur in humans. They should help physicians and public health officials determine the safety of a community living near a substance emission, given the concentration of a contaminant in air or the estimated daily dose received via food or water. MRLs are based largely on toxicological studies in animals and on reports of human occupational exposure. 

Vallejo YE, Buisson B, Bertrand D, Green WN (2005) Chronic nicotine exposure upregulates nicotinic receptors by a novel mechanism. J Neurosci 25 5563-5572 Vemino S, Amador M, Luetje CW, Patrick J, Dani JA (1992) Calcium modulation and high calcium permeability of neuronal nicotinic acetylcholine receptors. Neuron 8 127-134 Vizi ES, Lendvai B (1999) Modulatory role of presynaptic nicotinic receptors in synaptic and non-synaptic chemical communication in the central nervous system. Brain Res Brain Res Rev 30 219-235... 

Further data on the effects of chronic inhalation exposure to 1,4-dichlorobenzene would be useful, especially because chronic exposures to 1,4-dichlorobenzene in the air, in the home, and the workplace are the main sources of human exposure to this chemical. Any further testing of the effects of chronic exposure to 1,4-dichlorobenzene via the oral route should probably be done at lower levels of 1,4-dichlorobenzene than those that have already been used in the NTP (1987) bioassay, and should focus on dose-response relationships involving the hepatic, renal, hematopoietic, central nervous system, and metabolic pathways. Data on the effects of chronic dermal exposure to 1,4-dichlorobenzene may be useful if dermal absorption and systemic distribution of 1,4-dichlorobenzene can be demonstrated from toxicokinetic studies, since chronic dermal exposure to 1,4-dichlorobenzene occurs as a result of bathing and showering in drinking water that contains low levels of this chemical in many U.S. communities. 

Animal data include a 76-week inhalation study in rats that did not result in cancer (Riley et al. 1980), a 2-year oral study in rats that resulted in renal cancer in males (NTP 1987), and a 2-year study in mice that resulted in liver cancer (NTP 1987). No data using the dermal route were located. Additional data via the inhalation route would be useful since chronic inhalation exposures to 1,4-dichlorobenzene in the air of the home and the workplace are the main sources of human exposure to this compound. No further studies via the oral route appear to be necessary at this time. Chronic-duration cancer studies via the dermal route may be useful since chronic dermal contact with 1,4-dichlorobenzene at low levels in drinking water occurs in several U.S. communities. 

The term plasticity has been used to emphasize the brain s responsiveness and ability to adapt to changing environmental input. The brain creates new brain cell synapses and prunes old ones in response to experience (Greenough et al., 1992 Weiler et al., 1995). Caged animals with limited opportunities for spontaneous activity will not develop as many neuronal interconnections as more free-ranging animals. It is doubtful that the brains of children would be any less responsive to the environment than those of rats. If environmental influences, such as the frequency and quality of communication, can influence brain development, chronic drug exposure should be viewed as potentially dangerous. In addition, the stimulants make children less spontaneous, reducing their interactions with the environment and hence their brain development. 

Badger TM, Huang J, Ronis M, Lumpkin CK. Induction of cytochrome P450 2E1 during chronic ethanol exposure occurs via transcription of the CYP 2E1 gene when blood alcohol concentrations are high. Biochem Biophys Res Commun 1993 190(3) 780-5. 

Stress reactions to occupational and community chemical exposures occur in both acute and chronic forms. Much of the literature pertaining to community reactions to chronic chemical exposures involves hazardous waste sites. By 1988, the Environmental Protection Agency (EPA) identified 29,300 sites needing cleanup. The EPA listed 950 of them on the National Priorities List, also known as the Superfund sites [Health Aspects of the Disposal of Waste Chemicals 1986 Upton et al. 1989). Several sources review the medical and environmental aspects of hazardous waste sites (Andelman and Underhill 1987 Committee on Environmental Epidemiology 1991 Epstein et al. 1982 Health Aspects of the Disposal of Waste Chemicals 1986 Petts 1994 Weisaeth 1984). The most common chemicals in these sites include trichloroethylene, lead, toluene, benzene, chloroform, polychlorinated biphenyls, and miscellaneous solvents (Upton et al. 1989). 

This study is evaluating the relationship of chronic lead exposure to adverse pregnancy outcome and infant development. The study draws upon a unique community surrounding a lead smelter, refinery and battery plant in Titova Mitrovica, Yugoslavia. Control subjects are being studied in Pristina, a non-lead-exposed town 40 km to the south. 

The first case is based on a hypothetical stream receiving a metal-poUuted source (for instance the outlet of a metal factory). In this case, metal concentration is expected to be driven by dilution, being higher under low-flow than under base-flow conditions and minimum during floods. Metal accumulation is expected to be maximum under low-flow conditions and proportional to the duration of this water scarcity situation. Chronic exposure will lead to community adaptation, which is often related to changes in species composition. Metals will therefore be bioaccumulated in fluvial biofihns and transferred to higher trophic levels in the fluvial food web. 

---