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Introduction
Published in Marcello Pagano, Kimberlee Gauvreau, Heather Mattie, Principles of Biostatistics, 2022
Marcello Pagano, Kimberlee Gauvreau, Heather Mattie
As an example, consider the way we monitor the water supply for lead contamination [26]. In 1974, the United States Congress passed the Safe Drinking Water Act, and its enforcement is a responsibility of the Environmental Protection Agency (EPA). The EPA determines the level of contaminants in drinking water at which no adverse health effects are likely to occur, with an adequate margin of safety. This level for lead is zero, and untenable. As a result, the EPA established a treatment technique, an enforceable procedure which water systems must follow to ensure control of a contaminant. The treatment technique regulation for lead – referred to as the Lead and Copper Rule [27] – requires water systems to control the corrosivity of water. The regulation stipulates that to determine whether a system is safe, health regulators must sample taps in the system that are more likely to have plumbing materials containing lead. The number of taps sampled depends on the size of the system served. To accommodate aberrant local conditions, if 10% or fewer of the sampled taps have no more than 15 parts per billion (ppb) of lead, the system is considered safe. If not, additional actions by the water authority are required. We can phrase this monitoring procedure in a hypothesis testing framework: We wish to test the hypothesis that the water has 15 ppb or fewer of lead. The action we take depends on whether we reject this hypothesis, or not. According to the Lead and Copper Rule, the decision depends on the measured tap water samples. If more than 10% of the water samples have more than 15 ppb, we reject the hypothesis and take corrective action.
Analysis of blood lead levels of young children in Flint, Michigan before and during the 18-month switch to Flint River water
Published in Clinical Toxicology, 2019
Hernán F. Gómez, Dominic A. Borgialli, Mahesh Sharman, Keneil K. Shah, Anthony J. Scolpino, James M. Oleske, John D. Bogden
Flint, Michigan is a typical “post-industrial” community with a socioeconomic profile of a city at higher risk for childhood lead exposure from multiple sources. This has been true for decades prior to the drinking water switch from the Detroit Water Authority (DWA) to FRW that occurred from 25 April 2014 to 15 October 2015. The water source switch resulted in a higher percentage of households having tap water that exceeded allowable water lead concentration of 15 parts per billion, as outlined by the Lead and Copper rule of the Environmental Protection Agency [6–8]. Previous reports showed transient increases in the frequency percentage of BLLs of young children with BLLs above the current Centers for Disease Control and Prevention (CDC) reference value of 5.0 μg/dL [9–11]. An initial investigation compared percentages of childhood BLLs above the CDC reference value for 8.5-month periods of time before (2013) and during FRW exposure (2015) [9]. An investigation by Kennedy et al analyzed BLLs above the CDC reference value during four periods, including periods after issuance of a water advisory, and after the switch back to DWA from FRW [10]. Most recently, an investigation of BLLs in young children in Flint annually over a decade noted an increase in GM BLLs of 0.11 μg/dL from 2014 to 2015, with a subsequent decrease in 2016 [11]. However, the water switch was not confined to 8.5 months, nor a single calendar year, but rather took place over a period of 18 months [10]. In this investigation, we compare BLLs during the FRW change to two prior 18-month time-periods in order to place BLL changes, and the potential health impact on children during the FRW switch period, into an accurate historical and clinical context.