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CDC again tightens blood lead standard for young children: EPA’s action levels for lead in Butte soil now even more outdated

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Scour environmental cleanups across the nation and you’ll be hard-pressed to find one where it’s acceptable to leave as much lead in the yards of residences and school playgrounds as in Butte.

There are two reasons for this. The Atlantic Richfield Company, the primary party responsible for the Superfund cleanup in Butte, and the Environmental Protection Agency contracted studies in the 1990s feeding mine waste to rats and pigs and determined that lead in Butte soils comes predominantly from mine waste rock that has a relatively low bioavailability — it is not very absorbable by people, in other words.

The other reason is that in the model the EPA uses to set soil action levels at Superfund sites, the agency has since 1992 used as its standard 10 micrograms per deciliter as the blood lead level to avoid in more than 5% of children ages 0-5. That was the Centers for Disease Control and Prevention standard at the time, and it was based on the level at which adverse health effects were known to occur — at the time.

Now, as scientists say there is no safe lead-exposure level for children, both of those rationales for Butte's comparatively lenient standards are in for closer scrutiny.

In 2012, the Centers for Disease Control and Prevention changed its reference level for lead in a child’s blood from 10 μg/dL to 5 μg/dL. This October, the CDC further reduced its standard to 3.5 μg/dL.

The EPA has not stopped using 10 μg/dL.

The revised CDC reference levels were based on the estimate that 97.5% of children ages 1-5 in the country had blood lead levels below 5 μg/dL from 2007-2010, and below 3.5 μg/dL from 2015-2018.

But there's no question that the first reduction was also backed up by hard science on adverse health effects. This was the conclusion drawn by the U.S. Department of Health and Human Services’ National Toxicology Program report released in 2012:

“In children, there is sufficient evidence that blood Pb (lead) levels of 5 μg/dL are associated with increased diagnosis of attention-related behavioral problems, greater incidence of problem behaviors, and decreased cognitive performance as indicated by (1) lower academic achievement, (2) decreased intelligence quotient (IQ), and (3) reductions in specific cognitive measures.”

When EPA plugged the low bioavailability percentage and the 10 μg/dL level into its computer model back in 1992, the residential soil action level in Butte was set at 1,200 ppm, and has been there ever since.

This same number was used this summer to assess Butte schoolyards, and five of the properties came back hot for lead or arsenic or both by current standards. Those areas were slated for remediation, but more playgrounds would have to be remediated if the EPA lowered its numbers to line up with even the 2012 CDC target.

EPA vs. the rest

Most Superfund sites where lead is involved set the residential soil action level around 400 ppm, including Anaconda, where studies have shown lead bioavailability is high. Some cleanups use the default value for bioavailability, 30%, whereas it’s been determined by EPA to be just 12% in Butte. More generally, the EPA on its website recommends kids don’t play in bare soil with lead content over 400 ppm.

The Montana Department of Environmental Quality has adopted the 5 μg/dL standard in determining soil action levels for lead in cleanups. Assuming default bioavailability, the MDEQ used the EPA’s same model to determine a 200 ppm action level for residential soils. In California, the state requires 80 ppm or less in residential soil. A bill is in play in New York to restrict lead in residential soils to 300 ppm. It’s 250 ppm in Washington state.

Underlying the stricter standards being adopted around the country is something the EPA and the CDC have both been saying for a decade: There is no safe level of lead exposure for children.

Children can be exposed to lead because they crawl around in the dirt and put things in their mouths. At the same time, they absorb more lead than adults because they’re developing body systems and detoxification processes. Lead can permanently impair cognitive abilities and cause other health effects. Even low levels of lead in the blood of children can result in lower IQ and hyperactivity, slowed growth, hearing problems and anemia — that’s straight from the EPA handbook.

So the question is: Why does the EPA still use a risk assessment standard designed to prevent 5% of a population’s children from reaching a blood lead level of 10 μg/dL when the CDC has said currently only 2.5% of the nation’s children have a blood lead level above 3.5 μg/dL?

Change forthcoming?

EPA Region 8 officials said the agency is reevaluating its lead policy nationwide. The EPA has been doing so for almost a decade, but a new lead initiative has now been proposed at the national level.

“The one thing that I do know is that EPA is very closely and for quite a while examining the lead policy," said Charlie Partridge, EPA toxicologist for Region 8, which includes Butte.

If there is a change, it would be to lower the lead standard the EPA uses, Partridge said, something that would impact Superfund sites across the country.

“If the EPA does make the decision that the best for the environment and human health is a new target blood level, thousands of sites across the nation are going to revisit this,” Partridge said.

Region 8 officials provided The Montana Standard the contact for Jackie Harwood, senior advisor in the EPA headquarters' office of public affairs. A voicemail message and email were left Tuesday afternoon, and the Montana Standard didn’t receive a response.

Under the leadership of President Joe Biden and new EPA Administrator Michael Regan, The EPA on Oct. 28 released a draft strategy to reduce lead exposures nationwide. It is up for public comment until Jan. 26.

In the document, the EPA lists goals to revise lead policy at sites governed by Superfund law to “protect human health and the environment in accordance with the latest science” and specifically “revisit the soil-lead hazard standards.”

Eric Hassler, director of the Butte-Silver Bow Reclamation and Environmental Services Department, is in charge of the county’s role in the Superfund cleanup. The primary mechanism for remediating lead from Butte residences is the Residential Metals Abatement Program, run by Butte Silver-Bow and paid for by Atlantic Richfield through Superfund agreements.

RMAP has been removing soils laden with high lead levels since the late 1980s, and dust from attics since the early 2000s.

Hassler said the EPA should take a hard look at the 10 μg/dL number.

“Yes. I think science should drive the action levels,” he said. “I’d like the EPA to land on a final blood lead level that corresponds with the others.”

Say the EPA plugged 5 μg/dL into its model, and left everything else the same. Partridge, Nikia Greene, EPA’s remedial project manager for Superfund in Butte, and Montana Tech professor David Hutchins, a long-time advocate for stricter lead action levels, did just that at a meeting in August 2020.

They found the residential soil action level would be 410 ppm. The model has changed some, but considering 3.5 μg/dL is the latest CDC reference level, it’s worth examining what a 400 ppm action level would mean for Butte.

Hassler’s team at RMAP ran the numbers.

Every residential property in Butte Priority Soils Operable Unit, which encompasses Uptown, must be assessed and remediated if it exceeds action levels. If the soil action level changed to 400 ppm, the yards of an estimated additional 1,433 properties would have to be remediated.

That’s a lot more work. It would be costly, and that cost would have to be negotiated in Superfund agreements. Already, the RMAP still needs to assess around 600 properties in the BPSOU and re-assess about 800 more due to a change in sampling policy that occurred in 2011. An additional 8,000 residences outside the BPSOU also became eligible for the RMAP last year. Although the program isn’t required to actively seek participation outside the BPSOU, interest has been high.

Some additional remediation of the schools assessed this summer would be required also in the event the target was lowered.

Atlantic Richfield contractors undertook assessment of yards and playgrounds of 21 properties children frequent in Butte this past summer, most of those schools.

Four had sections that failed the current lead standard, and those areas were slated for remediation.

If the 400 ppm action level was used instead of 1,200 ppm, an additional playground at the AWARE Early Head Start on Mercury Street would have to be remediated, and an additional playground at the Head Start location on North Clark Street, as well as four playgrounds at the Head Start location on Arizona Street. There, lead as high as 1,020 ppm was detected in the top 2 inches of soil in a playground.

Butte Central Elementary-Middle School also exceeded the 400 ppm mark in all three sections sampled in the courtyards, testing at 798 ppm for lead in the top two inches of soil in the yard encompassing the majority of that outdoor space.

Under the EPA’s current target, those spaces are still considered to be protective without remediation.

Various outdoor spaces in lower profile areas would also have to be remediated, but the majority of schoolyards tested below 400 ppm across the board.

Medical monitoring

Whether the EPA’s action levels are protective, and whether the RMAP program is making a difference in Butte are two separate questions, but there is some overlap.

Though RMAP only remediates soil that hits that 1,200 ppm mark, the county’s biomonitoring effort takes 500-700 pin prick screening samples from Butte children annually through the federal Women, Infants and Children program, although this came to a halt during the COVID pandemic. This is also part of Superfund.

Responding to the CDC’s recommendation, the county has considered 5 μg/dL an elevated blood level since 2013, and targets homes of any child who tests above that for immediate environmental assessment through RMAP — if the elevated blood level is confirmed through follow-up venous sampling, which doesn’t always occur. However, all participants in the biomonitoring program are encouraged to seek an environmental assessment, especially if metals threats are identified in the interview process.

These assessments go beyond mining related impacts — lead, arsenic and mercury in soil, indoor dust and attic dust. They also evaluate whether other impacts may be at play, such as lead-based paint and lead in silverware.

Even then, soils in yards are only remediated if they hit 1,200 ppm.

In the process, Butte has built a large lead information database over the years, which is used in medical monitoring reports to evaluate the efficacy of remediation.

These studies have shown blood lead levels of Butte’s young children have improved dramatically over the years remediation has been done, and in fact average blood lead levels were in line with national levels once adjusted for housing age and demographics as of 2010.

The National Health and Nutrition Examination Survey that looks at lead nationwide stopped adjusting for housing age after that, so comparisons between Butte and other parts of the nation with older houses are now harder to draw. Old houses often have lead paint.

The percentage of children with elevated levels is still significantly higher in Butte compared to the nation overall, however.

The second RMAP medical monitoring study reported that in 2004, almost 40% of Butte children screened had blood lead levels above the 5 μg/dL reference level, and 65% above the 3.3 μg/dL detection level, as opposed to almost 10% at 5 μg/dL and 22% at 3.3 μg/dL nationwide.

Butte declined more rapidly than the national average after that, reaching about 6% above 5 μg/dL and 27% above the 3.3 μg/dL detection limit by 2016, compared to under 2% at 5 μg/dL and about 5% above the 3.3 μg/dL detection limit nationwide.

Those numbers have to be taken with a grain of salt, because the pin prick method used by WIC in Butte for screening has a tendency to turn out false positives, according to Hassler and others involved in reporting. It’s also worth mentioning a batch of those tests was recalled during the pandemic — when WIC wasn’t doing any sampling in Butte — over concern the machines were instead producing false negatives.

The NHANES survey, meanwhile, uses only venous blood confirmations, which are much more reliable, but also more invasive.

Rosalind Schoof, toxicologist for engineer consulting firm Ramboll, authored the RMAP medical monitoring studies. Can we trust that 27% of young kids in Butte had blood lead levels over 3.3 μg/dL, while nationwide, it was only 5%?

Schoof, prefacing that the national numbers aren’t weighted for housing age and demographics, said she believed the comparison between Butte and the national average was fairly reliable.

“My general impression of the Lead Care II kits (used in Butte) is that they're probably fairly accurate in detecting values above 3.3. But the exact values may not be as reliable,” she said.

Butte-Silver Bow confirms elevated blood levels with venous follow-ups whenever possible, but has run into problems getting cooperation from families. Sometimes pin pricks also pick up lead contamination on a child’s hands. These challenges should be resolved when a new position is filled in the health department — funded by Atlantic Richfield through Superfund — which will enable quicker confirmation samples.

If the RMAP program again lowered its medical monitoring standard for elevated blood levels to 3.5 μg/dL in accordance with the CDC, it would lead to a steep increase in environmental assessments resulting from follow-ups. This could help drop blood lead levels in Butte, and also provide more data on what’s causing Butte to have a higher frequency of elevated blood lead levels than the national average.

But it wouldn’t make up for protective soil action levels.

The EPA folks are often quick to mention lead paint and lead pipes whenever the topic of mining impacts are brought up.

RMAP follows up on every case of a blood lead level elevated above 5 μg/dL that’s confirmed with a venous blood draw with case management. But many times venous confirmation doesn’t happen — skewing data and sometimes preventing an environmental assessment.

Hassler said RMAP’s case management investigations have never identified lead pipes to be the principal cause, and RMAP hasn’t deemed lead paint to be the most likely source of an elevated blood lead level in over five years.

RMAP’s annual construction completion reports show elevated blood lead levels were confirmed by venipuncture in children through monitoring 57 times from 2013 to 2019. Many times, guardians didn’t see the follow-up all the way through to the point a cause could be detected, and sometimes no environmental assessment could be done at all.

The presence of lead-based paint was noted in 16 cases. Attics tested hot for lead in 10 cases, soil was hot in five cases, and indoor dust was hot in four cases. Specific causes not related to mining impacts, such as lead in dishware, were identified in four cases. There were multiple lead risk factors at play in many of the cases.

So the multi-pathway method has certainly helped children in Butte, but it doesn’t necessarily indicate that causes unrelated to mining present a higher risk to kids than mining impacts.

Another notable finding in the RMAP medical monitoring reports was that rates of elevated blood levels in Butte are consistently higher in warmer months when kids are more likely to be playing outside.

It’s an important tool, but there is significant uncertainty involved in biomonitoring. Participation is voluntary — many children are never tested — and venous confirmation is hard to pull off, whereas cleanup of every property in the BPSOU older than 1982 to EPA action levels is required by law.

It’s a big ask to understand just how children are being exposed to lead. Part of the reason is that overall exposure has dropped massively nationwide in recent decades.

A 40-year analysis of NHANES surveys found the average blood lead level of a child in this country was 15.2 μg/dL from 1976 to 1980. It was 0.83 μg/dL from 2011 to 2016. That’s a 94.5% decrease.

Butte’s blood lead levels have rapidly declined with the rest of the country. The CDC attributes nationwide decline mostly to phasing out leaded gasoline, leaded paint and lead in food and other products.

But a unique and serious lead problem remains in Butte. In the yards RMAP samples in Uptown Butte, soils have come back hot 40% of the time.


The contamination in Anaconda is from smelter dust, which is more absorbable due to process and finer particulate size, while the contamination in Butte is from mine waste — that has been the EPA’s line on bioavailability, and there’s a heap of research behind it.

But attic abatements started in Butte in the early 2000s. RMAP crews have found that 95% of the hundreds of homes assessed were hot for lead in attic dust, and 57% for both lead and arsenic.

So where did that dust come from?

“I would say, in all likelihood, the majority probably is coming from an aerial deposition scenario. And the major aerial deposition scenario would probably be smelter releases. But there is some wind-blown component as well,” Partridge said.

In an email exchange between the EPA’s Greene and Hutchins, Greene explained that “roasting and smelting in Butte declined significantly in the early 1900s with construction of smelters in Anaconda and Great Falls.”

The Washoe Smelter in Anaconda ran until 1980. Could the dust that contaminates nearly every Butte attic be from that smelter? Could that same more bioavailable dust be in Butte soils?

None of the bioavailability studies looked primarily at residential soil. If residential soil was used, it was generally mixed with soil from waste rock dumps. In fact, the express purpose of some of the studies was to look at waste rock so it could be compared to the bioavailability from smelter dust in Anaconda. Still, Greene and Partridge defended the research on grounds the most probable exposure scenarios were studied and determined to be from the mine waste stream, and that some residential soil was used in the studies, and that all of the soil studied would have had whatever was deposited from the air in it as well.

A bioavailability study of the attic dust in Butte has never been done, but the EPA uses the higher default bioavailability percentage for dust action levels in Butte.

For Hutchins, there is enough mystery remaining in the bioavailability picture to warrant a more conservative approach in at least one factor in the EPA’s action level equation.

The obvious choice is a switch from 10 μg/dL to the current CDC reference level, he said.

The bottom line

This story is really about whether it’s safe for children to have a blood lead level of 5 μg/dL. It’s not.

That the EPA bases its soil action levels in Butte off a 10 μg/dL target is a danger to Butte’s children, any way you try to look at it.

Partridge said it’s a big job changing action levels for so many projects across the nation, but he didn’t say whether the EPA was going to do it.

Atlantic Richfield’s contractors took the time to go into Butte schools to sample the soil and create remediation plans this year, almost a decade after the brass at the EPA started wondering if they should change its target blood lead level to correspond with every other agency of health, and just before the CDC again dropped its target.

It’s notable that the worst soil problems were found at the Head Start facilities, where young, low-income children play. In an interview, Schoof pointed out that poverty may be a factor in why Butte kids have higher blood lead levels than the national average. Perhaps in this case, poverty and mining impacts are not independent of one another.

Outside Superfund sites, the EPA tells parents to keep their kids out of bare soil with over 400 ppm lead. Because Butte’s been designated a Superfund site, the parties responsible for the mess treated Butte to extensive studies that justified lowering that level and reducing the cleanup.

There have been perks along the way, and Hassler and Greene may have a point when they say RMAP could lose some of its personal touch — working around folks’ construction plans, and being able to further investigate the odd case of a child chewing on batteries. That if the numbers drop too low, it could turn into old fashioned dig-and-haul.

But if you plug 3.5 μg/dL into the EPA’s model, and leave bioavailability for Butte where it is, you get a lot less than 400 ppm.

That’s the direction the country is headed, because there’s no safe level of lead exposure. It’s more than fair to ask if Butte’s being left behind.

Note: Local officials from the EPA, Butte-Silver Bow and Atlantic Richfield promptly responded to interview requests and provided data for this story.


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