USGS scientist Peter Van Metre examines a parking lot where coal-tar sealcoat has been applied.A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

What is sealcoat?

Coal-tar-based sealant is the black liquid sprayed or painted on many parking lots, driveways, and playgrounds.

Several PAHs are probable human carcinogens, and many are toxic to fish and other aquatic life. Coal tar, which can cause cancer in humans, is made up of more than 50 percent PAHs. An estimated 85 million gallons of coal-tar-based sealant are used on parking lots and driveways each year, primarily in the central and eastern United States.

What are the rates of PAH emissions to the air from coal-tar-based sealcoat?

Coal-tar-based sealants are emitting PAHs into the air at rates that could be greater than annual emissions from vehicles in the United States based on a study in which USGS scientists tracked PAH levels in air and in dried sealcoat following sealcoat application to a parking lot. Two hours after sealcoat application, PAH emissions were 30,000 times higher than those from unsealed pavement. In a second study, USGS scientists measured PAHs in air above parking lots with and without sealcoat, in suburban Austin, Texas. Parking lots with three- to eight-year-old sealant still released 60 times more PAHs to the air than parking lots without sealant.

A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

Children living near sealed parking lots are exposed to PAHs

Children living near coal-tar-sealed pavement are exposed to twice as many PAHs from ingestion of contaminated house dust than from food, according to a separate new study by Baylor University and the USGS. Baylor University scientist Spencer Williams used USGS measurements of PAHs in house dust to estimate the potential ingestion of PAHs by young children living near coal-tar-sealed parking lots. Ingestion of PAHs from food has long been thought to be the primary route by which children are exposed to PAHs. PAH ingestion by children living near coal-tar-sealed parking lots  is estimated to be 14 times higher than by children in apartments adjacent to unsealed parking lots.

Sealcoat is a major source of PAHs to the environment

Past and current  research on environmental contamination and coal-tar-based pavement sealants and implications for human health and stormwater management are summarized in a new Feature Article in the journal Environmental Science and Technology. The article is jointly authored by researchers with the USGS, Minnesota Pollution Control Agency, University of New Hampshire, City of Austin, Texas, and Baylor University.

Bans on coal-tar sealcoat

Some governments have taken action on the use of coal-tar-based sealcoat.  Fifteen municipalities and two counties in four states (Minnesota, New York, Texas and Wisconsin), the District of Columbia and the state of Washington all have enacted some type of ban, affecting almost 10.4 million people. Several national and regional hardware and home-improvement retailers have voluntarily ceased selling coal-tar-based driveway-sealer products.

Coal-tar sealcoat compared to asphalt-based sealcoat

USGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

Two kinds of sealcoat products are widely used: coal-tar-based and asphalt-based.  The coal-tar products have PAH levels about 1,000 times higher than the asphalt products. Coal-tar-based sealcoat is more commonly used in the Midwest, southern, and eastern United States. Asphalt-based sealcoat is more commonly used in the western United States.  Consumers can determine whether a product contains coal tar by reading the product label or the associated Materials Safety Data Sheet (MSDS), available from the applicator, retailer or on the Internet.

For more information, please visit the USGS website on PAHs and sealcoat, or contact Jennifer LaVista.

Young boys working in a newly cropped field in Africa.

In parts of eastern Africa, drought is of increasing concern, as poor families suffer from food shortages and the inability to grow crops and sustain livestock. Stunted growth in children due to malnutrition has also been linked to climate trends in Africa.

Drought conditions are expected to continue as global temperatures continue to rise and rainfall declines across parts of eastern Africa.

This poses increased risk to millions of people in Africa who currently face potential food shortages.

What’s being done to help?

The USGS is involved in a variety of research efforts to help understand current and future conditions in Africa, helping to inform plans to provide aid.

The Famine Early Warning Systems Network, or FEWS NET, is one endeavor that has already made great strides in helping to address this issue. FEWS NET helps target more than $1.5 billion of assistance to more than 40 countries each year.

FEWS NET examines the populations of the developing world with the most food insecurity, identifying critical situations in which food aid will be needed. These are populations whose livelihoods are typically tied to subsistence rain-fed agriculture and pastoralism.

FEWS NET is sponsored by the U.S. Agency for International Development (USAID) Office of Food for Peace and the USGS is actively involved.

FEWS NET at the United Nations Climate Convention

A USGS presentation on FEWS NET will be a featured side event on November 30, 2011, at the United Nations 17^th annual Conference of the Parties (COP-17) in Durban, South Africa. The convention’s purpose is to develop international agreements and a declaration of policies and practices for combating climate change and its impacts around the world.

A herder moves cattle through a barren landscape in eastern Africa.

Climate forecasts and remote sensing help spot future trouble

FEWS NET has developed its own climate services to provide decision makers with early identification of agricultural drought that might trigger food insecurity. Scientists use climate forecasts to develop forward-looking food security assessments that are based on expected agricultural outcomes for the season ahead.

Since networks of ground observation stations are often sparse or reported late in FEWS NET countries, satellite remote sensing of vegetation and rainfall fills in the gaps. Remote sensing from space allows for rapid, accurate assessments of a broad range of environmental and agricultural conditions. USGS scientists provide the technologies and expertise to support remote sensing for FEWS NET activities.

Early warning of famine in Somalia helps pre-position food supplies

On July 20, 2011, the United Nations declared parts of Somalia as a region of famine. The decision was supported by FEWS NET and USGS observational evidence of conditions in the area.

The declaration was the culmination of early warning communications encouraging — months before the crisis — that government and other agencies pre-position food and supplies in the region.

“None of the many uses of Earth-observing satellites is more vital — or has as much potential for prompting timely humanitarian intervention — as famine early warning,” said USGS Director Marcia McNutt. “Remote sensing from space allows USGS scientists to provide rapid, accurate assessments of a broad range of environmental and agricultural conditions.”

The eastern Horn of Africa, the continental region that encompasses Somalia, has experienced two consecutive seasons of very poor rainfall resulting in the worst drought in 60 years. Crops have failed, livestock deaths are widespread, and food prices are very high. While the rains this winter have been good, food prices remain high, and the food security situation remains insecure.

Stunted growth linked to malnutrition and climate change

Other USGS research is helping to identify the impacts of a changing climate on Africa’s people. Scientists recently discovered that malnutrition and dry hot living conditions are linked to stunted growth in Mali, West Africa.

USGS research found that Mali was becoming substantially warmer and a little bit drier. Scientists also knew that farmers and those who make a living raising sheep, cattle, goats, or camels were poor, and that stunted growth was occurring throughout Mali.

Scientists wondered if there could be a link between human health and increasingly warm and dry conditions.

To investigate, the USGS worked with the University of California, Santa Barbara, to study climate observations and demographic and health data. The Demographic and Health Survey program routinely compiles data from surveys in 90 countries to study trends in health and population. Scientists analyzed statistics on specific villages in Mali and found that there was a link between a warmer climate and increased stunting.

Population growth combined with the impacts of warming will further increase these health impacts.

Stunting was also linked to other factors, such as mother’s education and the water supply system. Women’s education, improved water supplies, and agricultural development could help to address malnutrition and stunting in Mali.

An article on this research was published in in the journal, Applied Geography, by San Diego State University, the University of California, Santa Barbara, and the USGS.

A Food Security Assessment in Somalia found severe impacts on livestock due to drought conditions.

Other studies underway

Other new research includes the discovery that the warming of the Indian and western Pacific oceans (which is linked to global warming) affects rainfall over large areas of the Horn of Africa. As the globe has warmed over the last century, the Indian Ocean and western Pacific have warmed especially fast.

The resulting warmer air and increased humidity over the Indian and western Pacific oceans produce more frequent rainfall in that region. The air loses its moisture during rainfall, and then flows westward and descends over Africa, leading to decreased rain in parts of eastern Africa. Trends toward increased frequency of drought that we are seeing now are likely to continue into the future as warming continues.

A few recent articles on this research were published in the journal, Climate Dynamics, by scientists with the USGS, the University of California, Santa Barbara, and Los Alamos National Laboratory. The most recent article concludes that global warming will lead to a decrease in rainfall during the summer monsoon season, from June to September, across southern Sudan, southern Ethiopia, and northern Uganda.  Another article concluded that eastern Africa, particularly Kenya and southern Ethiopia, will also have a significant decrease in rainfall during the long-rains season from March to June.

USGS scientists are working hard to translate these technical studies into reports for decision makers. To date, they have completed summary fact sheets focused on Sudan and Kenya.

Scientists also found that some regions, like northern Ethiopia, are not getting drier due to current warming temperatures. Rainfall varies dramatically across all of eastern Africa, with high mountainous areas typically receiving many times the rainfall received in low-lying areas. Therefore, agricultural growth in these climatically safe regions could help offset rainfall declines in other locations.

Start with science

Scientists are looking at clues and changes in nature to understand the impacts of global warming. In Africa, impacts are seen across the landscape — on farms and even in humans.

By starting with science, well-informed decisions can be made to help Africa as it faces drought, famine, and health concerns.

FEWS NET partners include the USAID, Chemonics International, the USGS, NASA, NOAA, and the USDA. The Geography Department at the University of California, Santa Barbara, is a partner to the USGS in this effort.

Want more information?

Listen to a podcast interview with USGS scientists as they discuss ongoing efforts to understand conditions in Africa.