Abstract: In May 2012, the CDC adopted a new sliding scale reference value for childhood lead poisoning, reducing the former 10 µg/dL benchmark by half. Using Massachusetts (MA) as a model state, we estimated the change in the population of 9–47 month-olds at risk for lead poisoning. We then examined the impact of the 5 µg/dL reference value on the demographic characteristics of lead risk in MA communities. We find that the new CDC benchmark will lead to a 1470 % increase in childhood lead poisoning cases among 9–47 month-olds in MA, with nearly 50 % of the examined communities experiencing an increased prevalence of lead poisoning. Further, the top 10 MA communities with BLLs ≥5 µg/dL have significantly fewer foreign-born residents and sig...