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Biomedical subjects

J Fawell

Publications and source records attributed to J Fawell.

7 recordsLinked to original sources
PubMed2001

Use of routinely collected data on trihalomethane in drinking water for epidemiological purposes.

OBJECTIVES: To explore the use of routinely collected trihalomethane (THM) measurements for epidemiological studies. Recently there has been interest in the relation between byproducts of disinfection of public drinking water and certain adverse reproductive outcomes, including stillbirth, congenital malformations, and low birth weight. METHOD: Five years of THM readings (1992--6), collected for compliance with statutory limits, were analysed. One water company in the north west of England, divided into 288 water zones, provided 15,984 observations for statistical analysis. On average each zone was sampled 11.1 times a year. Five year, annual, monthly, and seasonal variation in THMs were examined as well as the variability within and between zones. RESULTS: Between 1992 and 1996 the total THM (TTHM) annual zone means were less than half the statutory concentration, at approximately 46 microg/l. Differences in annual water zone means were within 7%. Over the study period, the maximum water zone mean fell from 142.2 to 88.1 microg/l. Mean annual concentrations for individual THMs (microg/l) were 36.6, 8.0, and 2.8 for chloroform, bromodichloromethane (BDCM), and dibromochloromethane (DBCM) respectively. Bromoform data were not analysed, because a high proportion of the data were below the detection limit. The correlation between chloroform and TTHM was 0.98, between BDCM and TTHM 0.62, and between DBCM and TTHM -0.09. Between zone variation was larger than within zone variation for chloroform and BDCM, but not for DBCM. There was only little seasonal variation (<3%). Monthly variation was found although there were no consistent trends within years. CONCLUSION: In an area where the TTHM concentrations were less than half the statutory limit (48 microg/l) chloroform formed a high proportion of TTHM. The results of the correlation analysis suggest that TTHM concentrations provided a good indication of chloroform concentrations, a reasonable indication of BDCM concentrations, but no indication of DBCM. Zone means were similar over the years, but the maximum concentrations reduced considerably, which suggests that successful improvements in treatment have been made to reduce high TTHM concentrations in the area. For chloroform and BDCM, the main THMs, the component between water zones was greater than variation within water zones and explained most of the overall exposure variation. Variation between months and seasons was low and showed no clear trends within years. The results indicate that routinely collected data can be used to obtain exposure estimates for epidemiological studies at a small area level.

Analysis of Variance↗
PubMed2000

Risk assessment case study--chloroform and related substances.

Chlorine, used as an important disinfectant for drinking water, can react with naturally occurring organic matter to form chloroform, bromodichloromethane, chlorodibromomethane and bromoform. Chloroform and other trihalomethanes have been shown to increase tumours of the liver, kidney or large intestine in rats or mice. The risk to man from these contaminants must be assessed carefully since there is considerable benefit associated with the use of chlorine. The weight of evidence suggests that chloroform is non-genotoxic and there are data, for each site, to indicate that tumours only occur at high doses where there is also tissue damage. Bromodichloromethane has also been shown to increase liver and kidney tumours but this and bromoform have been shown to increase large intestinal tumours in rats. The weight of evidence is that they are only weak genotoxins and they do not appear to be active in vivo. It is probable that the mechanism for the liver and kidney tumours is the same as for chloroform but the mechanism for the large intestinal tumours is uncertain. However, the toxicity and carcinogenicity of these substances is profoundly affected by dosing in corn oil. New studies suggest that dosing in drinking water would not result in increases in tumours. The evidence suggests that the use of a threshold approach, based on a tolerable daily intake, would be the most appropriate way of determining safe levels in drinking water.

Animals↗
PubMed2000

Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review.

OBJECTIVES AND METHODS: Chlorination has been the major disinfectant process for domestic drinking water for many years. Concern about the potential health effects of the byproducts of chlorination has prompted the investigation of the possible association between exposure to these byproducts and incidence of human cancer, and more recently, with adverse reproductive outcomes. This paper evaluates both the toxicological and epidemiological data involving chlorination disinfection byproducts (DBPs) and adverse reproductive outcomes, and makes recommendations for future research. RESULTS AND CONCLUSIONS: Relatively few toxicological and epidemiological studies have been carried out examining the effects of DBPs on reproductive health outcomes. The main outcomes of interest so far have been low birth weight, preterm delivery, spontaneous abortions, stillbirth, and birth defects--in particular central nervous system, major cardiac defects, oral cleft, and respiratory, and neural tube defects. Various toxicological and epidemiological studies point towards an association between trihalomethanes (THMs), one of the main DBPs and marker for total DBP load, and (low) birth weight, although the evidence is not conclusive. Administered doses in toxicological studies have been high and even though epidemiological studies have mostly shown excess risks, these were often not significant and the assessment of exposure was often limited. Some studies have shown associations for DBPs and other outcomes such as spontaneous abortions, stillbirth and birth defects, and although the evidence for these associations is weaker it is gaining weight. There is no evidence for an association between THMs and preterm delivery. The main limitation of most studies so far has been the relatively crude methodology, in particular for assessment of exposure. RECOMMENDATIONS: Large, well designed epidemiological studies focusing on well defined end points taking into account relevant confounders and with particular emphasis on exposure characterisation are ideally needed to confirm or refute these preliminary findings. In practice, these studies may be impracticable, partly due to the cost involved, but this is an issue that can be put right--for example, by use of subsets of the population in the design of exposure models. The studies should also reflect differences of culture and water treatment in different parts of the world. To identify the specific components that may be of aetiological concern and hence to fit the most appropriate exposure model with which to investigate human exposure to chlorinated DBPs, further detailed toxicological assessments of the mixture of byproducts commonly found in drinking water are also needed.

Chlorine↗