Document LJVyaVROZGoa15p7o7qG7Nwkw

GUIDELINES FOR DRINKING-'*' * " 0HATr' Vohj me / 'om ations 4. CHEMICAL AND PHYSICAL ASPECTS 51 this document are based upon the selection of an acceptable risk or less than I additional case of cancer per 100 000 population assuming a daily consumption of 2 litres of drinking-water by a 70-kg man. The cancer risk associated with other concentrations of these substances can be readily calculated. 4.1.3.4 Apportionment of intake Drinking-water is not the only source from which man is exposed to many of the chemical constituents for which guideline values have been set. In many cases the intake from drinking-water may be small in relation to the intake from food and air. It was accepted that, in the evaluation of the health elTects of inorganic constituents, all routes of exposure (air. food, and water) had to be considered when deciding upon a value for drinking-water. This, in some cases, proved to be problematical because of the lack of information concerning the biological availability of the contaminants present in foodstufTs. However, in the case of chemicals for which carcinogenicity is the main concern and for which the guidelines have been based upon lowdose extrapolation techniques in order to equate the recommended value with an incremental cancer risk, other sources of exposure have not been considered. The incremental risk from food. air. occupation, etc., will be additional to that from drinking-water. As regards pesticides, a special situation exists. In this case, the ADI has already been "used up*' in setting tolerances for pesticide residues in foods. On the other hand, measurable quantities (although usually at very low concentrations) arc frequently found in drinking-water. Therefore in setting guideline values for pesticides in drinking-water, vatues were generally based on committing not more than 1 "i of the ADI. This was considered acceptable on the grounds that not all food will contain pesticides at the permitted tolerance levels. 4.2 Health-retated inorganic constituents A scries of working papers dealing with the health effects of 37 in organic constituents occurring in drinking-water were studied in order to decide upon guideline values for the undesirable inorganic substances in drinking-water (Table 7). 4.2.1 Guideline values recommended On the basis of the health-related data concerning the 37 inorganic constituents examined it was decided that, at the present time, guidelinevalues could be recommended for only 9 of them (Table 8). and the evidence is summarized in section 4.2.2. However, since the effects on health of several other constituents in the list are the subject of current debate, brief explanations of the i / CAPCO JEN 0010437 Consul want tunxrmxn antimony KMrtiC ^ uomoc btnum ban^ium boron Cx*n<um Chromium cobrt coopm cy*ndt (rrocyanKi* fl wono# hr0nti* (c^oum and rn*gn**<wm) iron IMd Irthium mtgntaum mang inn* fnrrcury mo^rboon^n fl*Ckf nnnti rutnta K^r *o6vn lllfunm thtJUym thocrn*f# ten titanium tungsten uranium vanadium one Gud*in Vftiltt* Mt X X X X X X X X X document draft ad X .X X X X X X X X X X X X X X X ftatenad for C4nwCJr*iion of MtihriiC and Organo<Olie atoacn X No tenon ttQUiltd X X X X X X X X X X X X X X X X X X X X X reasons why guideline values could not be recommended are also provided in section 4.2.2 for 7 other constituents. Eight of the constituents listed in Table 7. although not of direct health concern, could have an indirect effect upon health because of their effect on the aesthetic quality of drinking-water. These substances arc dealt with later under "Aesthetic and organoleptic aspects** (page 77). CAPCO JEN OOI0438 4. CHEMICAL AND PHYSICAL ASPECTS Table 8. Guideline values (or health-related inorganic constituents 53 ConttituM *r*nic ddnuun Chromium fiuCKO* fn*fCufy niiut* u* N) M^ium * Cu flWi** ^rr vry flop--YbiWQ t/pon Gutffelint v(v (mgrlitr**) 005 0005 0.05 01 1.5* 005 0001 1000 001 ** co'WMTP'pieon 4.2.2 Summaries of the evidence used in setting guideline values 4.2.2.1 Arsenic Based on human health data, a concentration of 50 p g of arsenic per litre is not associated with any adverse health effects. Estimates have been made of the risk of cancer from tow intakes of arsenic, but these arc very uncertain. At an arsenic concentration of 50 pg/litre. the contribution made by water to the total intake will normally be about one-half to two-thirds; for very low dietary intakes of arsenic, the proportion provided by water may be somewhat higher. Arsenic in drinking-water will normally be the main source of inorganic 3rsenic. An arsenic concentration of 0.05 mg, litre is recommended as a guideline value. *i 4.2.2.2 Asbestos The health hazards associated with occupational exposure to airborne asbestos have been well documented. Epidemiological studies suggest that prolonged inhalation of asbestos also leads to an increased incidence of cancer of the gastrointestinal tract; however, it is not known whether such an effect is systemic or results from swallowing in haled fibres. The harmful effects of swallowed asbestos on human health h^ve not been determined. Studies in progress should permit a more complete evaluation of any hazard resulting from the swallowing of asbestos, but available data are, at present, insufficient to determine whether a guideline value is needed. 4.2.2.3 Barium There is no firm evidence of any health effects associated with the normally low levels of barium in water. Even at a barium concentration \\ \\ \ i CAPCO JEN 0010439