1,4-dichlorobenzene exposure potential

Several chlorophenols, including 2,5-dichlorophenol, have been identified in laboratory animals exposed to lindane. This indicates that the presence of 2,5-dichlorophenol is fairly specific, but not completely specific, for 1,4-dichlorobenzene exposure. Information on the analytical methods commonly used to detect and quantify 1,4-dichlorobenzene in biological samples is presented in Section 6.1. There are currently no data available to assess a potential correlation between the values obtained with these measurements and the toxic effects observed in humans or laboratory animal species. 

Children who are exposed to 1,4-dichlorobenzene would probably exhibit the same effects as adults, although there is very little information on how children react to 1,4-di chlorobenzene exposure. Thus, all health effects observed in adults are of potential concern in children. 

Deseriptive data are available from reports of humans exposed to 1,4-diehlorobenzene by inhalation (and possibly dermal contact). It is important to note that the case studies discussed in this section should be interpreted with caution since they reflect incidents in which individuals have reportedly been exposed to 1,4-dichlorobenzene, and they assume that there has been no other exposure to potentially toxic or infectious agents. There is usually little or no verification of these assumptions. Case studies in general are not scientifically equivalent to carefiilly designed epidemiological studies or to adequately controlled and monitored laboratory experiments. Thus, the case studies described below should be considered only as providing supplementary evidence that 1,4-dichlorobenzene may cause the reported effects. 

Quantitative absorption studies are not available for 1,4-dichlorobenzene in either humans or animals. This compound has some structural similarities to benzene and the smaller chlorinated aliphatics, and is thus assumed to be 100% absorbed when administered orally. Available data on 1,4-dichlorobenzene itself shows that under specific conditions, about 20% was absorbed via inhalation during a 3-hour exposure period. The potential for dermal absorption has not been assessed. 

In addition, several studies in animals have demonstrated that increased mortality can result from acute-, intermediate-, or chronic-duration oral exposure to 1,4-dichlorobenzene. Because 1,4-dichlorobenzene mothballs are used in many homes, they are often readily accessible in closets and storage areas. Therefore, there is a potential concern for the lethal effects of 1,4-dichlorobenzene, especially if accidentally consumed by young children. 

Further analysis of the results of the NTP (1987) bioassay has raised certain questions as to the relevance of the observed renal tumors in male rats and hepatic tumors in mice to the potential carcinogenicity of 1,4-dichlorobenzene in humans. The observation that kidney tumors are induced in male but not female rats in response to exposure to chemicals in addition to 1,4-dichlorobenzene has been the focus of recent... 

These values are currently under review by EPA and have not been included in the IRIS (1998) database. It is not likely, based on the potential for human exposure data presented in Chapter 5, coupled with the NOAELs and LOAELs gathered from human case reports and laboratory animal studies, that levels of 1,4-dichlorobenzene in the drinking water in any location would be high enough to cause a concern for cancer in humans. 

There is little credible scientific information available on the susceptibility and toxicological effects of 1,4-dichlorobenzene in children. The risk for exposure is apparently high. A study by Hill et al. (1995) measured blood levels of 1,4-dichlorobenzene and urine levels of its metabolites in 1,000 adults, finding that exposure to 1,4-dichlorobenzene was widespread, with 98% of the adults having measurable concentrations of 1,4-dichlorobenzene metabolites in their urine. There is no evidence to indicate that children are likely to be exposed to lower amounts of 1,4-dichlorobenzene from everyday living, suggesting that children are perhaps equally at risk for exposure and potential toxic side-effects. 

No data have been located relating to carcinogenicity in humans exposed to 1,4-dichlorobenzene via inhalation, orally, or dermally. Epidemiological studies which used occupational exposure data would be useful to elicit such information on human exposure and potential cancer risks to 1,4-dichlorobenzene. 

Exposure. It is possible to measure 1,4-dichlorobenzene and its metabolite, 2,5-dichlorophenol, in blood, adipose tissue, and urine (Bristol et al. 1982 Jan 1983 Kimura et al. 1979 Langhorst and Nestrick 1979 Pagnotto and Walkley 1965 Pellizzari et al. 1985). Additional data with which to correlate these measurements to exposure levels, particularly by the inhalation route, and the potential health effects, would be useful. 

Reliable evaluation of the potential for human exposure to 1,4-dichlorobenzene depends in part on the reliability of supporting analytical data from environmental samples and biological specimens. In reviewing data on 1,4-dichlorobenzene levels monitored or estimated in the enviromnent, it should also be noted that the amount of chemical identified analytically is not necessarily equivalent to the amount that is bioavailable. The analytical methods available for monitoring 1,4-dichlorobenzene in various environmental media are detailed in Chapter 6. 

There have been no measurements of the levels of 1,4-dichlorobenzene or its metabolites in amniotic fluid, meconium, cord blood, or neonatal blood to investigate prenatal exposure. Consumption of breast milk can potentially expose nursing infants to 1,4-dichlorobenzene. Dichlorobenzene (all isomers) was detected in 100% of 42 samples of human breast milk collected in 5 urban areas of the United States at concentrations ranging from 0.04-68 ppb however, concentrations of 1,4-dichlorobenzene were not specified (Erickson et al. 1980). Dichlorobenzene (all isomers) was also identified in human breast milk in 8 of 12 women who were residents of Bayonne, New Jersey (6 women) Jersey City, New Jersey (2 women) Bridgeville, Pennsylvania (2 women) and Baton Rouge, Louisiana (2 women) however, concentrations of... 

There are some parental exposures to 1,4-dichlorobenzene that might result in potential exposures of children to this chemical. 1,4-Dichlorobenzene is not genotoxic and, thus, there should be no concern about exposure to parental germ cells (see Table 2-3 and 2-4 for further information). Additional... 

Those individuals living or working near industrial facilities or hazardous waste sites with higher than average levels of 1,4-dichlorobenzene in the air would have the potential for above-average exposures. 

In addition, individuals using space deodorants (air fresheners), toilet block deodorants, or moth repellents (moth balls or crystal) containing 1,4-dichlorobenzene in their homes have the potential for high exposure to this compound (Scuderi 1986). Indoor air concentrations resulting from the use of these products in bathrooms and closets have been measured at levels up to 1.3 mg/m (0.22 ppm) (Scuderi 1986). 

Dichlorobenzene has also been shown to be accumulated by terrestrial plants (Wang et al. 1996). No data were located on biomagnification of 1,4-dichlorobenzene through terrestrial or aquatic food chains. Additional information on bioconcentration of 1,4-dichlorobenzene by commercially important fish, shellfish, and plant species and biomagnification would be helpful in evaluating the potential importance of food chain bioaccumulation to human exposure. 

Tang et al. (2005) have reported significant levels ofVOCs in many supermarkets and department stores. In particular, the ratio of indoor to outdoor concentrations of 1-4 dichlorobenzene was as high as 39 in a store where leather products are used, 77.8 in a store that sells luxury fashion items and clothing, and 39 in a supermarket that sells household supplies. These observations demonstrate that consumer goods are potential sources of indoor VOC exposure. 

Dichlorobenzene is an eye, skin, and upper respiratory tract irritant in animals. It also affects the liver and kidneys and is considered a potential carcinogen. The oral LD50 is 500 mg kg in rats and more than 2gkg in rabbits. The lowest-observed-adverse-effect level (LOAEL) is 155 mg kg per 2 years of intermittent exposure in rats and mice. 1,4-Dichlorobenzene and a primary metabolite were negative in the mouse in vivo micronucleus test. 

Differences in species and possibly strain susceptibility to the renal effects of nitrobenzene exposure may exist, but their relevance to the potential renal effects in humans is not clear. The occurrence of renal effects in male rats, but not female rats or mice of either sex, in response to exposure to chemical toxicants is not unique to nitrobenzene. These differences have also been found with exposure to 1,4-dichlorobenzene, isophorone, and unleaded gasoline (Charbonneau and Swenberg 1988) and have been attributed to the production of high concentrations of the protein alpha- 2 i -globulin in the kidneys of male rats, but not in female rats, mice, or humans. These observations suggest that the severe renal effects observed in male rats exposed to nitrobenzene will probably not occur in exposed humans. 

The proposed restriction on 1,4-dichlorobenzene (1,4-DCB) illustrates the process. Concerns over the potential toxicity of this compound first surfaced under the Dangerous Substances Directive. The European Commission subsequently assessed the risks from exposure to 1,4-EXZB under the Existing Substances Regulation, beginning in the mid-1990s. 

The preceding chapters used brief case studies to illustrate key points. This chapter examines the life cycle of four substances in greater detail. Three of these substances, orthonitrochlorobenzene, 1,4-dichlorobenzene, and hexa-chlorobenzene, share a basic chlorinated benzene structure. The degree of chlorination and the presence of other functional groups affect their properties, usage, fate and transport in the environment, and (eco)toxicity. These substances also differ in their uses, which influences the potential for exposure. The remaining case study examines microbeads, a product whose size determines in part its life cycle. 

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