The emergence of COVID-19 marked a dramatic shift in our lives: quarantine, remote work, and coping with the extraordinary loss of life on a global scale. As environmental health experts, we were also concerned about how increased exposure to cleaning chemicals – and chemicals generally – might impact COVID outcomes. We knew this virus – like many of these chemicals – would not affect people equally but would put the most marginalized (like farmworkers, low-wealth communities, and the Global South) at greater risk.
Many chemicals, such as fluorinated chemicals (like PFAS) and phthalates, have been linked to harming the immune system (e.g., how capably your body responds to an external threat) and/or respiratory system (e.g., the risk of developing asthma). We recognized the need to identify, organize and curate data and evidence on environmental contaminants and developed a systematic evidence map to identify studies looking at how environmental chemical exposures can make people more susceptible to the effects of coronavirus-related immune and respiratory health outcomes. This map was done to support work by the California Office of Environmental Health Hazard Assessment (OEHHA) and other entities.
Systematic evidence maps use a transparent and systematic approach to identify, organize, and present the available data on an identified topic; the process is the same as gathering evidence for a systematic review. These maps have been used by National Institute of Environmental Health Sciences (NIEHS) Division of National Toxicology Program (DNTP) and The Endocrine Disruption Exchange (TEDX) and other scientists/researchers to identify data gaps for further exploration, by funders to identify potential areas to support, by the public to understand how a chemical of concern has been studied, and by policymakers to guide health-protective action.
Gathering the Evidence
Gathering the evidence is like doing the first steps of a systematic review, but we do not evaluate the evidence or synthesize it to draw conclusions. The aim is to identify the evidence, extract the key data and then visualize it. This is an important first step in understanding the extent to which there is available scientific evidence to understand how chemical exposures can increase susceptibility to COVID and other related viruses.
We created and pre published a protocol that outlined our Population, Exposure, Comparator, Outcome of interest (PECO Statement) and the methods that would guide the development of the SEM.
We developed a list of chemicals that might impact the respiratory and immune systems and are policy priorities for the State of California. Those chemicals primarily belonged to three classes:
- Per- and polyfluoroalkyl substances (PFAS) – pervasive “non-stick” chemicals used in household and cleaning products that can harm the immune system
- Pesticides – such as neonicotinoids, which are bee-killing pesticides that may affect children’s health
- Phthalates – “plasticizers” used in products like food and facemasks that have been linked to increases in allergic and infectious diseases
We used emerging data on coronavirus since it was a new disease and established data on similar respiratory viruses like SARS (2002 edition), MERS, and Influenza to see how:
- Susceptibility increases your chance of catching respiratory viruses (e.g., having asthma)
- Severity affects your likelihood to have severe forms of the disease, potentially be hospitalized, or die
- Vaccine Efficacy influences whether a vaccine protects you effectively
After running the searches on PubMed for these exposures and outcomes, and sorting through ~10,000 (!) study titles and abstracts and reading through ~2500 full studies to determine which ones to include for data extraction.
We extracted information for each of our included eligible such as study type, study location, and specifics around exposure and outcome (Were people exposed more than once? Did they have their blood collected? When were the exposure or outcome measured?).
After collecting this information in DistillerSR, we wanted to transform it into something digestible. This is where the map comes in.
Mapping the Evidence
Creating the evidence map in Tableau, a data visualization software, involved both scientific and design expertise.
We wanted to make sure our map was accessible to a wide variety of users and showed trends in the evidence instead which cannot be seen when looking across academic databases. At the same time, we included enough detail to inform scientists who might explore the evidence we were mapping.
Our systematic evidence map, allowed our end user to see and filter:
- If the study evaluated humans, animals, or both
- The specific chemicals, chemical classes, or outcome(s) evaluated
- The life stage the study examined
- Whether the study evaluated impacts on children, or marginalized populations like workers and low-wealth communities
- If the funders or authors had a financial conflict of interest
The goals of this systematic evidence map are to:
- Highlight evidence that can be used for environmental policy advocacy
- Identify populations at higher risk of COVID and other related infectious diseases
- Identify data gaps for further academic exploration
- Better inform COVID-related activities and prepare for future pandemics
We found 75 studies that evaluated how chemicals can influence the immune/respiratory system and thus be a potential risk factor for coronavirus susceptibility, COVID severity, or vaccine efficacy. By making systematically reviewed evidence more accessible, we hope to provide valuable information to better identify risks to the population and encourage more evidence-based environmental health research to inform policies that fairly and justly address problems like the COVID pandemic.
About the Authors
Swati Rayasam, MSc is a science associate at PRHE on the Science & Policy team. Swati uses PRHE’s specific expertise to write public comments to regulatory agencies and support evidence-based, health-protective chemical policy.
Chanese A. Forté, PhD-PhD, MPH was an assistant research scientist at PRHE on the Research and Science & Policy teams. Her research focuses on developmental neurotoxicants like pesticides and how they affect the developing fetus and how regulatory science can incorporate more New Approach Methods like cell culture studies.
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