Watch Your Step: Lead Lurking in the Soil

Thursdays are one of my favorite days of the week. Not because the weekend is approaching, but because it is when the UW Department of Environmental and Occupational Health Science seminar series takes place. Each week, an outside speaker joins us to discuss his/her research. I often leave inspired, with broadened interests, and a renewed excitement and passion for the environmental health field.

This week was no exception. I had the privilege of hearing Dr. Howard Mielke discuss his area of expertise: lead contamination in cities.

Lead has been front and center in the news recently. From the tragedy in Flint to emerging concerns about lead contamination in schools around the country, we are all now highly aware of the fact that our water supply may not be appropriately protected from outdated and dangerous lead pipes.

However, Mielke’s presentation did not focus on lead pipes. Nor the other common exposure source that I was familiar with, lead paint. Instead, he emphasized lead in soil.

Digging into the facts about lead in soil

How did lead end up in the soil?

Leaded gasoline.

Before leaded gasoline was phased out in the US in 1996, lead was emitted from tailpipes as a volatile compound (PbBr2) but quickly reacted to form a non-volatile compound (PbSO4) that precipitated to the ground (for more on the atmospheric chemistry of lead, see here and here). Thus, for years, we had millions of cars spewing lead not only into the air but also onto the ground all around us.

These automobile-related lead emissions resulted in several trends, including:

Such widespread lead contamination in the soils around our homes was a surprise to me, and these distinct patterns emphasize the terrible, lingering legacy of leaded gasoline.

But, could this really be an important exposure source, given all of the attention on lead paint and pipes?

Part of answering this question involves understanding that child blood lead levels exhibit a well-documented seasonal pattern: higher levels in the summer, and lower levels in the winter.

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[from Laidlaw et al, 2016: Children’s Blood Lead Seasonality in Flint, Michigan (USA) and Soil-Sourced Lead Hazard Risks]

What could account for this variation? Mielke and others suggest that in the summer months, children spend more time outside, playing in the yard. Lead-contaminated soil ends up on their hands, on their faces, and, likely also, in their mouths. In addition, soil dust tends to be drier in the late summer and can be easily inhaled. The observed seasonal patterns suggest that lead in soil accounts for a large part of child lead exposure. If lead paint were the main source of exposure, then we would probably see peaks in the winter, when kids are cooped up inside.

A solution for soiled soil?

While replacing leaded pipes seems like a tall task, eliminating lead in the soils around us feels even more overwhelming. Mielke has led efforts in the New Orleans area to bring in clean dirt to layer on top of lead-laden dirt (for example, in children’s playgrounds). But widespread implementation of massive soil-shifting projects seems unlikely.

Perhaps a better solution is to invest in emerging bioremediation techniques, using plants and microbes?

Big picture, though, Mielke advocates for a “Clean Soil Act,” analogous to our Clean Water Act or Clean Air Act, to provide the appropriate protections for the earth beneath our feet. (In fact, he helped develop a Clean Soil Act for Norway).

In the meantime, parents should be aware of this often overlooked source of child lead exposure. In addition, it is important for urban gardeners take appropriate precautions, since lead and other heavy metals can be absorbed in plants – thereby posing potential risks through dietary intake. (For more on heavy metals in gardens, check out Environmental Health Perspectives’ Urban Gardening: Managing the Risks of Contaminated Soil)

A lesson from the past?

In closing, I’ll share one of my favorite slides from Mielke’s presentation (see image below).

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He displays a quotation from Yandell Henderson, a Yale professor who vehemently protested against adding lead to gasoline during a hearing in 1925. He warned that society was at a crossroads, facing “the question whether…the action of the Government is guided by [scientific] advice; or whether commercial interests are allowed to subordinate every other consideration to that of profit.”

Unfortunately, we know how that particular story ended up.

And while there have been numerous similarly discouraging stories in the realm of chemicals and children’s health, I’m still hopeful that one day soon, our country will be ready to take the other road – prioritizing public health and environmental protections over profits.

Domestic legislation with international implications?

Take a look at these three world maps. Does anything stand out to you?

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For interactive versions of these maps, visit the Synergies Among the Basel, Rotterdam, and Stockholm Conventions webpage (also the source for these static images)

 

Maybe the uninspiring shade of grey that covers the United States in each one?

Yes, that’s what caught my attention as well.

These maps indicate member countries for the Stockholm Convention, the Rotterdam Convention, and the Basel Convention, respectively. The Stockholm Convention aims to eliminate or restrict Persistent Organic Pollutants, or “POPs,” which are toxic chemicals that persist in the environment and build up in organisms. The Rotterdam Convention promotes open exchange of information about specific pesticides and industrial chemicals. And, the Basel Convention focuses on the management of hazardous waste. Member countries (indicated by color coding on each of the maps above) can participate and negotiate in the relevant discussions. The United States, along with countries such as South Sudan, Myanmar, Iraq, and Uzbekistan, has not officially ratified the treaties.

The obstacle to forward movement on this issue is Congress (surprise, surprise). As with any international treaty, approval requires the “advice and consent” of two thirds of the Senate. But before this vote can take place, Congress needs to amend existing federal laws – the Toxic Substances Control Act (TSCA), the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and the Resource Conversation and Recovery Act (RCRA) – so the U.S. is able to comply with the treaties (for example, to give EPA the authority to regulate chemicals listed). Over the years, several relevant amendments have been proposed, but none have passed..

The chemicals regulated in these treaties are among the worst of the worst – dioxins, PCBs, DDT, as well as several multi-syllabic pesticides – and they tend to migrate long distances through wind, water, and biological organisms. EPA needs to have the ability to take appropriate actions on these chemicals, and others added in the future, to protect public health and the environment.

By abstaining from the treaties, the U.S. cannot negotiate for the addition of other dangerous compounds that may pose serious health risks to our population. (These chemicals do not respect borders, and pollutants released across the world can travel and cause harm here. The Alaskan Artic region is especially vulnerable). And, although U.S. taxpayers contribute to the Global Environment Facility – a fund that provides grants to assist countries on specific environmental improvement projects, including many related to the clean-up of POPs – we have no input on the use of these funds, since we are not members of the convention.

TSCA reform is currently under negotiation in the Senate and House, and while there have been intense discussions about many key components of the bill (such as state-preemption), minimal information is available regarding potential implications for these international treaties. However, it is crucial that the final legislation include such provisions, thereby paving the way for the U.S. to participate meaningfully in discussions regarding global chemicals of concern.