How is Our Health Impacted by the Physical Environment? — BrainPost | Easy-to-read summaries of the latest neuroscience publications

A first look at health-environment interaction

In 1854, John Snow made history investigating the connection between the Thames River and cholera epidemics. He found that the areas of London supplied with water contaminated by sewage were associated with high rates of cholera compared with those supplied by clean water. His epidemiological work represents one of the most famous cases of environmental health being linked with human health. As environmentalism gained attention and traction through the 20th century, researchers, activists, and health practitioners began to focus on the relationship between human health and the environment. For example, since the 1980s, researchers have been investigating the relationship between hormones in the environment and developmental disorders. More recently, research has advanced from examining the connection between the environment and communicable or inter-generational diseases to how environmental contamination and degradation negatively impact human mental and neurological health.

The impact of the environment on mental health can be viewed along a continuum. Sudden disasters (like an earthquake) might have a large, immediate impact while more gradual processes (like drought, climate change, or pollution) might affect health over time. One 2009 study in Western Australia found dryland salinity (the accumulation of salt in surface soil; a gradual process) was associated with an increased risk of hospitalization for depression. The results could indicate a causal relationship, or it could be that there is simply a correlation between soil salinity and socioeconomic status, which impacts mental health. In a similar vein, it is difficult to tease apart the impact of environmental changes on mental health from rising anxiety and despair about environmental destruction and the potential impact on our bodies. Air, water, and land pollution have also been associated with psychiatric disorders. In one study conducted between the United States and Denmark, poor air quality was associated with increased rates of depression and bipolar disorder. However, isolating the impact of air quality on mental health is difficult due to the fact there is a relationship between urban environments in general and mental health.

While the relationship between the environment and human mental health is difficult to parse, a recent review explicitly drew attention to an important missing piece of the puzzle: pharmaceutical drugs used to treat human diseases and disorders are flushed down the toilet and end up in our water system. Without targeted methods at water treatment facilities to remove these pharmaceuticals, they are ingested via drinking water, which could change our neurobiology. Greater interdisciplinary research leveraging ecology to inform human health research is needed to better understand these relationships.

How can we learn about human health from the environment?

The idea of monitoring wastewater to track human health isn’t new and has recently been leveraged to track COVID-19 cases in the United States. In China, wastewater is also surveyed for a broad range of pharmaceuticals, including drugs such as antihypertensives (blood pressure medication), antimicrobials, antipyretics (fever medication), analgesics (pain killers), and anti-inflammatories. While methodologies to tie water levels of pharmaceuticals back to population health statistics are still being developed, these studies indicate the future potential of investigating wastewater to track health at a community level.

In addition to examining human wastewater, some researchers investigate certain wildlife populations as “sentinel species.” These organisms are exposed to similar chemical agents as many humans, and can serve as models for future risks and effects in humans. Creative experiments have used dogs to detect scat from sentinel species such as otters and mink, testing their excrement for contaminants such as pharmaceuticals, heavy metals, anthropogenic organic contaminants (such as microplastics), personal care products, and flame retardants. The behavior of wild animals can also be observed to assess potential pollutants, such as the nest abandonment observed in swallows in environments contaminated by pesticides like dioxins and pollutants like furans.

How do human medications impact the environment?

While the impact of pharmaceuticals on human and animal health is usually thoroughly investigated in the drug development process, potential environmental impacts are often poorly understood. Pharmaceutical usage has increased in recent decades. Nevertheless, there is a lack of studies investigating the impact of pharmaceuticals on wildlife. The impact is particularly concerning in areas of the developing world with growing pharmaceutical production industries, such as Pakistan. Downstream effects of pharmaceuticals may be different than their intended uses in mammals. For example, histamines are used as neurotransmitters by invertebrates, so antihistamines may inhibit neurotransmission in animals like lobsters. More research is required to better understand whether there is an impact of low-concentration cocktails of medications.

What are the long-term implications for human neuropsychiatric health?

In the final arc of the loop, researchers must establish the impact of low doses of pharmaceuticals on humans who are exposed to them in the environment. Many pharmaceuticals or personal care products are detectable at ultra-low levels in the environment, and there is some controversy over the pertinence of the low-dose effects on humans. However, of high importance is assessing the impact of low-dose pharmaceuticals on developing children, as early life exposure to antidepressants in animals has been associated with Autism-like phenotypes later in life. In the coming years, it will be important to establish 1) first, whether ultra-low concentrations of medications can contribute to the emergence of psychiatric conditions in humans, especially in children, 2) second, what areas have the highest dosages and, therefore risk, and 3) third, how neuroscientists, physicians, and psychiatrists can learn from ecological sciences to better understand how humans impact, and in turn are impacted by, the natural world.

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