It may be 25 years since the 1986 Safe Drinking Water Amendments, but a Washington Post article covering a report released by the Centers for Disease Control and Prevention suggests almost 15,000 homes in Washington, D.C. were still receiving water with heightened lead levels in recent years.
Babies and small children are most at risk from increased blood lead levels (BLL) and there is no safe minimum recognized. It is estimated that as BLLs increase from 0 to 10 ug/dL, the fraction of individuals with an IQ greater than 120 decreases from 9 percent to 3 percent. Those are small changes and underline how the effects of lead exposure are subtle and often not recognized without very precise measurement. The report says lead is rarely found in drinking water at the distribution point or well head; it most commonly enters the system through corrosion of plumbing materials containing lead. There are three factors that influence the level of lead in drinking water, and one of these was the culprit in DC.
The first is obviously the presence of lead in plumbing materials. Leaded service lines (LSL) connect homes to a central water main or run from the water meter to the home and are known to contribute to lead found in household tap water, according to the report. Homes built before the 1980s may have LSLs or copper pipes with lead-soldered joints. Homes built after the 1986 Safe Drinking Water Amendments have ËœËœlead-free” plumbing that may still contain up to 8 percent lead.
The second factor is changes to pH levels; a higher pH level results in lower lead levels. Lead also dissolves more readily in soft water than hard.
Thirdly, mineral scale on the inner surface of pipes and joints of older systems, particularly in hard water areas, prevents lead from leaching into drinking water.
So what went wrong in DC? Well, with the best of intentions, the water authorities introduced a disinfectant called chloramine into the water supply to reduce microbial contamination. Unfortunately, chloramine on its own degrades mineral scale resulting in increased lead leaching. After some years an additional inhibitor was added to protect the mineral coating and lead levels gradually decreased again. In addition the water and sewage authority began a program of replacing the LSLs between the mains and the meters, but only a portion of homeowners undertook the expense of replacing the section from the meter into their homes so the program was of limited success.
Lead is an extremely toxic metal and the study illustrates how difficult it is to remove lead contamination from in situ infrastructure. Even before the enactment of the EPA’s 1986 Lead and Copper Rule, only 10-20 percent of total lead exposure was due to its presence in water. As the report says, in the United States, most children with BLLs greater than 10 ug/dL have been exposed to residential lead paint hazards in older homes or lead-contaminated house dust and soil, not water supply. In the approximately 15,000 DC homes affected, the report estimates 859 children had BLL greater than 10 ug/ml, all of whom in some subtle way will have been affected by exposure to waterborne lead contamination.