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Appendix F Daily Permissible Intake, Reconsidered In 197l, an a<i hoc committee convened by the Bureau of Community Environmental Management, Public Health Service, DREW, proposed the con- cept of a daily permissible intake (DPI) to be used as a reference point for establishing policies to prevent childhood lead poisoning. 5 Based on the knowledge available at that time, the committee decided that blood lead levels should not exceed 40 yg Pb/dl and that the DPI for children should not exceed 300 yg Pb/day. Kehoe's balance studies, ^ carried out on adult volunteers, were used as a reference for establishing a daily lead intake which would result in levels <40 yg Pb/dl. In adults, Kehoe found an intestinal absorption rate of 10 percent for lead ingested in the diet. The one volunteer whose blood lead level did not consistently exceed 40 yg Pb/dl had a daily intake of approximately 600 yg Pb/day. Unfortunately, the studies on this volunteer were discontinued after 15 months. Therefore, the effect of chronic exposure to 600 yg Pb/day was not established. More recent evidence indicates that the absorption of dietary lead is approximately 50 percent in young children. Alexander^ found that an intake of 10 yg/kg/day resulted in a daily fecal excretion of 5 yg/kg/ day. Barltrop found that children with a fecal excretion of approximately 5 yg/kg/day had a geometric mean blood lead level of 20 yg Pb/dl with a range of ll-38 yg Pb/dl. Studies in suckling animals suggest that the intestinal absorption rate of lead from milk may be as high as 70-90 percent. ' These studies suggest that the absorption rate of lead in children less than one year of age may be higher than 50 percent. In addition, the brain of infant rats accumulates lead to a greater extent than the brain of adult rats. Based on this new information, the daily absorption of lead from diet can be recalculated. The caloric requirement of a three year old child weighing 15 kg is one-half of the caloric requirement of an adult weighing 70 kg. Tepper, cited in King, ^ reported that the average adult diet contained 220 yg Pb/24 hrs. If a three year old child consumed the same diet, reduced to one-half to meet his caloric requirements, his dietary lead intake would be ll0 yg Pb/24 hrs. Based on a dietary absorp- tion factor of 10 percent, the adult would absorb 22 yg Pb/24 hrs or 0.31 yg Pb/kg body weight/day ((220 x 10 percent) T 70 kg). Based on the dietary absorption factor of 50 percent, the child would absorb 55 yg Pb/24 hrs or 3.67 yg Pb/kg body weight (ll0 x 50 percent * by 15 kg). Thus, when dietary lead absorption is expressed in terms of body weight, it can be calculated that the child would absorb 12 times as much lead as an adult receiving the same diet. The safety of blood lead levels in the range of 25-40 yg Pb/dl has recently been questioned. Early hematologic changes can be seen in women and children when blood lead levels reach 25-30 yg Pb/dl. ' Neurologic changes have not been documented at this low level. No data are available relating blood lead levels to possible adverse effects in children less than one year of age. 49
Because of new evidence available in both human and animal studies, this Committee believes that the DPI should be recalculated. Specifically, consideration should be given to: 1. Lowering the currently acceptable blood lead level of 40 yg Pb/dl for children. 2. Accounting for a higher intestinal absorption rate in young children. 3. Allowing a "safety factor" for children less than one year of age, since no data regarding effects or absorption rates is known for this group. 4. Expressing the DPI on either a body weight (yg Pb/kg/day) or caloric (yg Pb/Kcal) basis. The World Health Organization, FAO, has recently recommended that lead intake in adults should not exceed 3.0 mg of lead per week (429 yg of lead per day).103 For a standard 70 kg man, this would be equivalent to 6.12 yg of lead per kg/day. 50
