The Sonoma County Department of Health Services only takes action with blood lead levels of 10 micrograms per deciliter or greater.
https://www.sonoma-county.org/health/services/clpp.asp

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Low blood lead levels linked to lower IQ in Italian kids.

https://www.environmentalhealthnews....q-italy-teens/
Jan 16, 2013

Lucchini, RG, S Zoni, S Guazzetti, E Bontempi, S Micheletti, K Broberg, G Parrinello and DR Smith. 2012. Inverse association of intellectual function with very low blood lead but not with manganese exposure in Italian adolescents. Environmental Research https://dx.doi.org/10.1016/j.envres.2012.08.003.



Synopsis by Cheryl Stein

Kids exposed to low levels of lead score lower on IQ tests, according to a study of junior high students in Northern Italy. The low levels found in the youths are typical of many European and North American countries, and are below the exposures that U.S. health officials established to identify kids at risk. Growing evidence suggests even low amounts of lead can harm developing brains.

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Exposure to lead at very low levels is linked to lower IQ in a study of junior high students in Italy.
At higher levels, lead's effect on IQ is well-known. This study is important because it is the first to show a connection between such low blood lead levels and reduced IQ.
The lead levels in the Italian youths ranged from 0.4 to 10.2 micrograms of lead per deciliter of blood (µg/dL). When their levels doubled, IQ dropped by about 2.4 points.
The results support the concern that even very low levels of lead exposure cause lower IQ. Even small drops in IQ may have significant public health implications.
In the United States, the current guideline is set to identify children whose blood levels are higher than 5 µg/dL. Parents are notified, and they work with public health professionals to identify sources of and reduce exposure to lead.
But many experts suspect that there is no safe level of lead exposure – that even levels below 5 µg/dL are harmful. The study's findings support the concern.
This cross-sectional study looked at 299 Italian children aged 11 - 14 years old. The children attended 20 different schools and had always lived in one of two locations in Northern Italy: Valcamonica, a historically industrial region with environmental exposure to various metals, including lead and manganese, or Garda Lake, a tourist area with limited industrial activity.
Blood and urine samples were tested for lead and manganese. The children took an IQ test, which measured general intelligence. Another test assessed 10 key behavior and emotional issues, including attention and impulsiveness. The children's residence, socioeconomic status, alcohol intake and hemoglobin were accounted for.
On average, blood lead levels were low at 1.7 µg/dL. The highest measured blood lead level was 10.2 µg/dL. This is noteworthy because, until May 2012, the blood lead action level in the United States was at 10 µg/dL.
These children had blood lead levels typical of children in many parts of the world. Even in this low exposure range lead had a negative effect on IQ: for every 2.7 µg/dL increase in lead, IQ fell by 3.5 points. It took only 0.2 µg/dL of lead to lose just 1 IQ point.
There was no effect of manganese exposure on IQ.