Study identifies hundreds of obscure - yet persistent - chemicals.

Apr 02, 2010

Howard, PH and DCG Muir. 2010. Identifying new persistent and bioaccumulative organics among chemicals in commerce. Environmental Science and Technology http://doi.dx.org/10.1021/es903383a.




2010-0322chemicaljars
Andy.Schultz/flickr

 

A new study suggests that hundreds of chemicals used commercially could persist and bioaccumulate, yet next to nothing is known about their actions and levels in the environment. Predicting exposures and if and how chemicals may pose a health threat is incredibly difficult. Now, researchers propose a unique way to screen and identify chemicals that may need further evaluation and monitoring.

 


Context

Every year new chemicals are designed and incorporated into consumer products to improve the quality and efficiency of our daily lives. However, sometimes the use of these chemicals leads to unintended consequences that can affect both human and environmental health. Predicting when and how these chemicals will pose such threats is one of the most difficult challenges that scientists and regulatory agencies face.

Government agencies are responsible for determining a chemical's safety. Each country handles it differently. In the U.S., the Environmental Protection Agency executes the Toxics Substances Control Act that governs the screening of chemicals for safe commercial use. In Canada, Environment Canada oversees chemical regulations.

In the past, links between chemical exposures and health effects have often been identified by chance or through long months and/or years of expensive research efforts. It took decades to determine that mercury was poisoning the inhabitants of Minimata Bay in Japan during the 1940s-60s. In the mid to late 20th century, years passed before anyone realized the organochlorine insecticide DDT was bioaccumulating and contributing to the decline in bald eagle populations.

Today, we know more about how chemical structure can affect a chemical's life cycle – or fate – in the environment. Yet predicting if a chemical may pose a health hazard from use in consumer products is still a difficult task. This is partly due to the complexities of determining if and how these chemicals may escape from the product(s). Another big challenge involves measuring  and identifying the chemicals and exposures that may occur. Expensive tests are required to determine the levels released from the diffuse and variable sources that fluctuate over time. 

What did they do?

The authors collected data on more than 22,000 chemicals that were used in commerce from 1986 to 2006. They gathered the information from U.S. and Canadian government databases, including the Canadian Domestic Substance List and the U.S. EPA Toxic Substances Control Act Inventory Update Rule database.

Using a computer software system, the chemicals and some of their degradation products were screened for their ability to persist and bioaccumulate based on chemical properties and chemical structures. Experts further evaluated those chemicals identified as high priority for other important properties the computer system could not distinguish.

From these analyses, the researchers determined which chemicals would likely persist in the environment. This included assessing how long the chemical would remain in the atmosphere if released into the air; how the chemical would partition between water, air, and organic material (e.g. soils, sediments, plants); and if the chemical would bioaccumulate in organisms.

The chemicals were further evaluated to determine whether their intended use and amount of use would likely result in release to the environment. For example, chemicals produced in low volumes for research purposes were removed from the list.

What did they find?

The assessment identified 610 chemicals as being potentially persistent and bioaccumulative in the environment. About 100 of them have been measured in the environment, and 47 are historically identified compounds routinely measured through monitoring programs.

The list includes flame retardant chemicals used in furniture and electronic products, anti-microbial chemicals used in lotions and soaps and stain- and grease-repellent chemicals used in a wide variety of products. Some of these chemicals have been measured well away from their areas of intended use – such as in the Arctic air, in whales and gulls and in wastewater in Canada.

Many are no longer produced in the U.S. for commercial use. However, some are still being used in products or remain in the environment.

Of those named, 62 percent were halogenated; that is, they contain either fluorine, chlorine, bromine or iodine atoms. These compounds are known to bioaccumulate and persist. For example, numerous organochlorine pesticides that were found to be hazardous had more than four chlorine atoms attached to the central aromatic hydrocarbon backbones  – one or more benzene rings, which is a chemical structure of six carbons arranged in a hexagon shape. Only after years of heavy use and application were the pesticides – such as DDT, dieldrin and chlordane – phased out due to health and environmental concerns, including risks of cancer, birth defects and reproductive and neurological damage.

What does it mean?

A large number of halogenated chemicals that may persist and accumulate are still being produced and used in products, but very little is known about their levels in the environment. Also unknown are any unanticipated health effects.

This study explained a unique method to accurately and more quickly screen chemicals for their environmental fate. The software programs and computer-based screening efforts could assist regulatory agencies to be more proactive in characterizing exposure risks for chemicals used in commerce.

Routine testing methods can detect many of the chemicals identified. Given the large number of them, the authors suggest that monitoring programs and researchers should look for some of the specific chemicals to determine how prevalent they are in the environment. To facilitate this, they provided a list of "priority" chemicals based on production volume, bioaccumulation and persistence.

Maybe equally important is that researchers identified 13 silicone-based compounds. Presently, there is no reliable method to detect them in environmental samples, so there is no way to know if the chemicals are contaminating soil, air, water or organisms.

There are significant concerns related to how chemicals are regulated under the existing Toxic Substances Control Act (TOSCA) implemented by the U.S. EPA.  Concerns over the use of proprietary chemicals in consumer products – that is, the identity of the chemical is unknown to the public – has prompted some advocacy groups to challenge the efficacy of the TOSCA program. In addition, many argue that TOSCA does not fully evaluate a large enough spectrum of potential health effects as part of its testing program.

Perhaps implementing more computer-based screening efforts would help revise chemical management plans and prevent widespread environmental and human exposures.

Resources

Muir, DCG and PH Howard. 2006. Are there new persistent organic pollutants? A challenge for environmental chemists. Environmental Science and Technology
40:7157–7166
.

Questions about pesticide environmental fate. Frequently asked questions. Extoxnet.

Toxics Substances Control Act. U.S. Environmental Protection Agency.

 

 

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