The New York Times (NYT) article is discussing a recent publication in the journal Environmental Health Perspectives related to “Project TENDR”, which stands for “Targeting Environmental Neuro-Developmental Risks”. In the NYT piece, statements of the Project TENDR group presented in the published paper are summarized and it is pointed out that this publication comes at the same time as the signing into law of the overhaul of the Toxic Substances Control Act (TSCA). The reporter states that the TENDR group wants the chemical industry to prove that a chemical is safe before it is marketed, in place of U.S. Environmental Protection Agency’s (EPA) authority to review all chemicals in commerce as stipulated under the updated TSCA law.
Unfortunately, the NYT’s article on the TENDR statement lacks scientific basis and is out of date. The reporter failed to discuss specific things that the new TSCA law accomplished, and how they relate to many of the concerns raised by the TENDR group. A prime example is that under the new law EPA will review all new chemicals and make an affirmative determination before they are allowed to enter commerce. In addition, all chemicals in commerce in the United States now will undergo a risk-based review by EPA for the first time. The EPA will be prioritizing chemicals for review, and there are strict deadlines that must be met by EPA in order to ensure compliance by chemical manufacturers. EPA will no longer consider costs and benefits when making a decision about the safety of a chemical; only health and environmental safety will be considered. Most importantly with respect to the issues raised by Project TENDR, EPA must consider whether vulnerable groups such as infants, pregnant women,children, the elderly, will be exposed to a chemical and, if exposure is expected to occur, then the risks to those specific groups must be assessed. Unfortunately, these provisions of the TSCA overhaul are not mentioned in the NYT piece, even though these changes to the existing regulatory system will require that both existing chemicals and new chemicals undergo scrutiny to determine if they might pose a risk to the brain of the developing organism.
The list of compounds described in the article and highlighted in the TENDR consensus statement includes some compounds well-recognized to pose a risk to neurodevelopment precisely because of the chemical testing and evaluation that was required as part of existing EPA regulations, an important point that is missing in the NYT article. For example, organophosphate pesticides have been around for many decades and have been required to undergo EPA registration since enactment of Unites States law in 1947 (i.e.., Federal Insecticide, Fungicide and Rodenticide Act or FIFRA). Similarly, among the other chemicals mentioned, lead, mercury and PCBs are already extensively regulated, while air contaminants such as PAHs, nitrogen dioxide and particulate matter are also specifically regulated under current programs at EPA. With all of the existing EPA programs, as science has advanced in our understanding of the process of human development and risks to infants and children, the testing of chemicals has evolved. Over the last 20 years, specific advances in chemical testing and risk assessment requirements by EPA have focused on risks to infants and children within the auspices of FIFRA, the Clean Air Act, and even generally with implementation of the program to examine endocrine-disrupting effects of chemicals in commerce. As a result, it is hard to understand how the TENDR consensus can use such examples as evidence that the current regulatory system “is fundamentally broken”. In fact, with enactment of TSCA reform, EPA has the tools it needs to review both new and existing chemicals, with a requirement to focus on risks to vulnerable populations such as infants and children.
Unfortunately, when discussing the issue of chemical exposure and risks to the developing organism, the fundamental principle of toxicology that underpins the effects that chemicals can have on living organisms, dose-response, is often ignored or even not considered. It is the dose of the chemical, and the pattern of exposure, that determines whether a chemical produces an adverse effect on an organism, not simply the presence of a chemical, even for developmental neurotoxicity. Just as a critical concentration at the site of action is needed before a drug can produce its beneficial effects in humans, the same principle applies to toxicity produced by any chemical. Effects that might be reported at high doses will not occur at lower doses if the concentration at the site of action falls below the threshold for toxicity. Evidence-based toxicology and epidemiology dictates that the dose of chemical is the critical factor when examining the risk posed by a chemical, not just its presence, even in the human body. Given that many of the epidemiological studies investigating the relationship between exposure to specific chemicals and conditions such as autism and ADHD, and referred to in the NYT article and the TENDR consensus statement, often suffer from a lack of exposure information during critical periods of development, any conclusions that can be drawn from such studies are limited by the lack of dose-response information.
Although the issues of autism and attention-deficit hyperactivity disorder (ADHD) are clearly issues of concern in medicine today, improvements in diagnostic methods and criteria for such diseases are acknowledged by the TENDR group to account for part of the purported increase in different forms of developmental neurotoxicity. When considered in light of the changes in TSCA that are now signed into law, there is no scientific basis for the assertion that the system in the United States is “fundamentally broken” as stated by the TENDR group. Instead, with new scientific developments in our understanding of the processes that regulate neurodevelopment in humans, and the new emphasis on risks posed to vulnerable human populations as part of chemical risk assessment at EPA, the regulatory system in place going forward should prevent the occurrence of the types of compound-specific problems (e.g., widespread lead exposure through air, food, and water) encountered in the last century.