Health Monitoring, Risk Assessment, and the Blood-Lead Reference Value


Last week the Association for toxic substances and disease registry, or ATSDR, began testing Anaconda residents for blood lead and urinary arsenic. ATSDR, in partnership with Anaconda-Deer Lodge Public Health Department and Montana Department of Public Health and Human Services, is conducting an exposure investigation and this biomonitoring is one of the first steps.

These initial tests were limited to 200 Anaconda residents, but a waiting list was established for future testing. The results will be delivered to those tested, as well as compiled into a report. If elevated levels are found, ATSDR will include recommendations for reducing exposure.

David Dorrian, environmental health scientist with ATSDR, was clear that this kind of testing only reflects recent exposure. “They are wonderful tools for informing public health. They have some limitations. They are a snapshot in time. They don’t necessarily tell us about the far past.”

ATSDR reports that arsenic is excreted within several days of exposure and the half-life of lead in blood is about a month. This is a serious limitation for a study of residents of a Superfund site who are concerned about a lifetime of exposure.

The samples collected will be analyzed and compared to national benchmarks. For lead, that benchmark is the Center for Disease Control’s blood lead reference value, currently set at 5 µg/DL. This is a level that the CDC uses to identify high-risk childhood populations, so steps can be taken to avoid further lead exposure. The reference level is pegged to the upper 97th percentile of the US blood level distribution for children aged 1-5. As blood lead levels continue to decrease, this reference value will be adjusted downward.

The CDC’s reference value is used in health monitoring, such as this study in Anaconda, but it is also used in other ways that relate to Superfund. In fact, the value was used in the original risk assessment here in Butte to establish our action levels, the lead concentrations found in soils and dust that would trigger a cleanup. With so much importance placed on this value I decided to investigate further.

I wanted to get the perspective of a risk assessment professional, so I called Aimee Reynolds of the Montana Department of Environmental Quality.

AR: “I am Ammie Reynolds and I am the contaminated site cleanup bureau chief, here at DEQ, I oversee a bureau that works on state Superfund and petroleum tank release sites, department of defense sites, and brownfields, but I’m also a risk assessor, I’ve been with DEQ for 26 years doing risk assessment.

I asked Aimee to help us understand how the risks associated with lead are evaluated.

AR: “A lot of the time with other contaminants we have to look at animal data and extrapolate that to what might happen in a human being. With lead, because unfortunately we’ve had lead-based paint and lead in gasoline for years and years, we have a lot of human data, and know what happens to lead when it gets into people’s bodies, and then what those health effects may be. So, the way we evaluate lead is using these health-based models, one of them I know you are familiar with, is the Integrated Exposure Uptake Biokinetic Model, which the acronym is IEUBK. That’s a model we use to evaluate lead in children, because children are the most impacted by exposure to lead. It accounts for exposure to lead in air and food and water and dust and we’re able to put that all together and see how much lead might end up in a child’s blood. And then that can help us decide what levels might not result in seeing health effects.”

I see, so in each case you’re looking at the most vulnerable population and going from there

AR: “The idea is that if you protect the kids, who are most vulnerable, then any health effects that an adult might see would show up at higher levels, and so we’re being protective of all the people, if we protect the people that are most vulnerable. “

Now as I understand it, this IEUBK model uses a threshold blood-lead level that is tied to the CDC’s blood-lead reference level, is that accurate?”

AR: “Yes, the way that the model is set up, is that you can put in an input value of blood-lead concentration into the model, and then run the model to determine what level in a particular media, usually it’s soil or dust, but you could do it related to water or air, or food, if you wanted to, you could determine what level would be likely to result in a certain percentage of the population, and you can set that in the model, too, to not have the concentration in blood-lead above which you think there might be health effects.”

Now, this gets complicated, because as mentioned, the CDC value is tied to national averages, and is periodically adjusted. When the lead risk assessment was conducted in Butte, the value was at 10 µg/DL, but was subsequently reduced.

AR: “Yeah, in 2012, the CDC did come out with a reference level of 5 ug/DL because they indicated they started seeing health effects in children at those levels, and they further go on, on their website, to really making an effort to see that blood-lead levels are as low as possible, to be safer.”

And that value will be reduced again. Recently, a CDC panel urged reducing it to 3.5 µg/DL. So the question arises: are action levels based on the old value still protective of health?  The EPA has been slow to address this concern. Since the value was reduced they have been promising it is under consideration. The Superfund process uses a 5-year review to assess cleanup progress at each site and to integrate new information, but so far, they have not revised the IEUBK model with the new value. And the health study will rely on the current value of 5 even though it could be reduced at any moment.

There is increasing evidence that there is no safe level, and efforts should be made to reduce any lead exposure. It can be hard for the residents of a Superfund site to know what is safe with seemingly arbitrary standards. Previous studies here in Butte have shown we are moving in the right direction with dramatically reduced blood [lead] levels. But it is in the public’s interest to stay vigilant and continue that trend.  So, stay tuned as we report on developments in the health monitoring and action levels in the coming months.

I’m Dave Hutchins reporting for KBMF.