Report No FR0290

R I Crane and M J Wilkinson

March 1992



To evaluate the relative contributions that exposure from different sources makes to total human intakes of certain organic chemicals.


The general public is exposed to a range of organic chemical contaminants via air, water, food, soil and other sources, and little is known about the patterns of such exposure. Information on the relative exposure from drinking water and other routes is needed to:

  1. allow appropriate proportions of an Acceptable Daily Intake (ADI) to be allocated to drinking water;

  2. put into context any potential health hazards posed by exposure to these chemicals through drinking water.


Patterns of exposure are very different for the three groups of organic chemicals considered here, namely pesticides, certain industrial chemicals, and by-products of drinking water disinfection.

For pesticides the main sources of intake are expected to be food and water, but there are insufficient data for food to allow comparative estimates of exposure to be made. It would appear that for the general public intake from water is associated primarily with herbicides and intake from food primarily with insecticides. In some instances, for example with atrazine, there may be justification in suggesting a higher allocation of the ADI to drinking water than the 10 % presently allocated.

None of the herbicides or other pesticides most frequently reported at elevated levels in UK drinking waters (most notably atrazine, chlorotoluron, isoproturon, MCPA (+MCPB), mecoprop and simazine) have particularly low Acceptable Daily Intakes (ADIs), suggesting that their presence is unlikely to present a toxicological hazard at the levels reported. A number of potentially hazardous industrial chemicals (solvents) were considered but these must not be considered to represent all industrial chemicals. For tetrachloroethylene, 1,1,1-trichloroethane, benzene and trichloroethylene the major route of exposure appears to be inhalation, whilst ingestion from food and water account for relatively insignificant proportions of total daily intakes (c. 1 % for water). However, for carbon tetrachloride and xylenes there are some indications that water (and food) may make a significant contribution, even though these chemicals have broadly similar properties and uses to the others. It is likely that these dif ferences arise at least partly from inadequacies in the available data, rather than real differences in exposure patterns. The public's exposure profile for drinking water disinfection by-products is different to that for other chemicals, because they a re generally not industrially important. Consequently drinking water accounts for the major part of total exposure for all the disinfection by-products studied, followed by air and then food. Although exposure from air can be significant this appears to result largely from inhalation following volatisation of the chemicals from drinking water, which may therefore be considered as the original source. Exposure to disinfection by-products can be significant for regular users of swimming pools. However, this is a special exposure route and cannot be considered as an important source of exposure for the general public as a whole.


Based upon the findings of this review the following recommendations are made:

  1. There is a need to quantify levels of certain pesticides in UK foodstuffs in order to enable the real significance of the most common drinking water contaminants to be determined.

  2. Consideration should be given to allocating a larger portion of an Acceptable Daily Intake (ADI) to drinking water for herbicides than for insecticides.

  3. Analysis of drinking water for the most toxic (to humans) pesticides is needed to confirm their absence at elevated levels.

  4. Exposure patterns for industrial chemicals must not be generalised but must be considered on a chemical (or chemical group) specific basis, and ADIs allocated accordingly.

  5. More data on the frequencies of occurrence and typical concentrations of hazardous industrial chemicals in drinking water would help balance published data, which tend in some cases to concentrate on particularly contaminated waters.

  6. The contribution to total intake from inhalation of disinfection by-products arising from drinking water needs to be elucidated.

  7. The greater part of the ADIs for disinfection by-products should be allocated to drinking water. This should include a consideration of (vi) above. Exposure in swimming pools needs to be considered as a special case.


This report individually reviews human exposure to 3 different groups of chemicals; namely pesticides, certain hazardous industrial chemicals and by-products of drinking water disinfection, each of which is considered in its own appendix. The relative contributions that non-drinking water sources (such as air and food) make to total intake of these chemicals are compared with those derived from drinking water.

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