Water Quality
1.
Recommended Guidelines
1.
Drinking Water
It is recommended
that the total concentration of chlorate in drinking water
should not exceed 2.4 mg/L to protect 5-kg infants.
Rationale:
This guideline is designed to protect 5-kg infants since they drink more water
in proportion to their body weight than adults do. The maximum daily intake
rate from all sources is 1 mg/kg body weight. Water consumption is assumed
to be 1.5 L/d, the normally accepted drinking water consumption rate for average
people in north temperate climates. The lowest doses reported as fatal in humans
are 2 g in small children and 5 g in adults or about 100 mg/kg. Applying a
factor of 0.01 to derive a no observed effect level (NOEL) from the acute fatally
toxic threshold gives a guideline of 1 mg/kg. This entire intake is not in
the water since there must be some allowance reserved for intake from food
and other sources. In the table below consumption ratio of about 70% in the
water and 30% from other sources is assumed.
Table 2. Body Weight and Safe Chlorate Concentration in the Drinking Water
| weight
in kg |
5 |
10 |
20 |
30 |
50 |
70 |
90 |
| [chlorate]
mg/L |
2.4 |
4.8 |
9.6 |
14.4 |
24.0 |
33.6 |
43.2 |
The calculation is 1 mg/kg X 5 kg = 5 mg/ 1.5 L/d = 3.4 mg/L X 0.7 = 2.38 mg/L
(rounded to 2.4 mg/L for 5 Kg infants). This leads to overprotection for
adults who are heavier but tend to drink about the same amount of water.
Doses in
excess of 100 mg/kg, 7 grams for a 70-kg adult human or 500
mg for a 5-kg baby, are generally fatal, although doses of
this magnitude are unlikely from ambient exposures.
