In 2003, FMC contracted an outside firm (Exponent) to investigate the actual human exposure to arsenic in soil in the Middleport area. During that summer urine and toenail samples were taken from 439 Middleport residents which included 77 children under 7 year old. This represented more than a quarter of the population in Middleport and a little less than half of the children under 7 who lived in the area at that time. Tests were also performed on samples of vegetables from area gardens, house dust was collected and soil samples analyzed. The detailed report from Exponent is in the document repository of this web site in the Arsenic in Soil - Related Documents.

It should be noted the government agencies have declined to accept the results of this study. The Community Input Group is seeking a clarification of the reasons.

Click the "Read Full Article" link below for the summary extracted from the FMC document "CMS Work Plan for the Air Deposition Area" also in the document repository of this site (See the story below "Corrective Measures Work Plan Now Available".)


The risk assessment process described above incorporates health protective assumptions to avoid underestimation of soil exposure. Biomonitoring studies, if available for the potentially exposed population, may provide a useful comparison to the theoretical exposures estimated in the risk assessment.

A comprehensive arsenic exposure and biomonitoring study was conducted during 2003 in Middleport (Exponent 2004). An independent panel of scientific experts from health institutes, universities, and the Centers for Disease Control and Prevention (CDC) provided oversight for this voluntary study and the findings were peer reviewed and published in the scientific literature (Tsuji et al. 2004). Because absorbed arsenic is rapidly excreted in the urine, arsenic exposure was assessed by measuring arsenic concentrations in urine. The researchers targeted young children whose exposure to soil is expected to be highest and conducted the study during the summer months when outdoor activities involving soil contact occur most frequently. Arsenic was also measured in yard soil, house dust, and garden produce for participating residents who elected to have such sampling.

Key findings of the Middleport biomonitoring study included the following:

Speciated and inorganic urinary arsenic levels (i.e., the forms relevant to assessing exposures to arsenic in soil) in Middleport residents were low.

Urinary arsenic levels were generally not correlated with soil or house dust.

House dust concentrations were not correlated with soil concentrations.

Specifically, all urinary arsenic levels for Middleport were below reference levels for speciated and inorganic arsenic in urine of 40 and 20 µg/L, respectively. The range in speciated arsenic concentrations was from 0.89 to 20 µg/L, with the highest concentration approximately half the reference level of 40 µg/L. The maximum inorganic arsenic level found in Middleport, 2.7 µg/L, was approximately one-quarter of the lowest reference level of 10 µg/L. There were no significant relationships between urinary arsenic and arsenic in soil. The only significant relationship between urinary arsenic and environmental media occurred between levels of speciated arsenic in creatinine-adjusted urine samples and house dust in young children. However, there was no significant relationship found between house dust concentrations and soil concentrations.

The Middleport biomonitoring study was designed to have the greatest chance of detecting any increased arsenic exposures associated with Middleport soil. Despite this design, no such association was detected, and urinary arsenic concentrations were found to be below reference levels and comparable to those of other populations without elevated soil arsenic concentrations.

The lack of increased exposure associated with arsenic in soil can to be attributed to three primary factors: 1) concentrations of arsenic in Middleport soils are low, 2)little soil is ingested by residents, and 3) arsenic in soil has low bioavailability. Furthermore, exposures to arsenic naturally present in drinking water and food are much higher than those from soil with concentrations of arsenic at Middleport levels.

The results and conclusions of the biomonitoring study will be considered in the CMS process and will be used in communicating and explaining risks to the community.