Agriculture Chemical Pollution

Chemical Pollutants: The Forgotten Killers

“As crude a weapon as the cave man’s club, the chemical barrage has been hurled against the fabric of life – a fabric on the one hand delicate and destructible, on the other miraculously tough and resilient, and capable of striking back in unexpected ways. These extraordinary capacities of life have been ignored by the practitioners of chemical control who have brought to their task no “high-minded orientation,” no humility before the vast forces with which they tamper.”
Rachel Carson, Silent Spring

I read the other day that pollution is now the leading killer of people worldwide, linked to an estimated 9 million premature deaths in 2015. That means that pollution in the soil, air, and water killed three times more people than those that died of AIDS, tuberculosis, and malaria combined and 15 times more individuals than those that lost their lives as a result of war and other forms of violence. So what are the pollutants responsible for such devastating effects? By and large chemical pollutants are the guilty parties here, but frustratingly they have been somewhat left on the side-lines in terms of media attention over the last few years. The vast majority of recent news articles, documentaries and blog posts (we too are guilty of this here at Seastainability) on the topic of pollution have focused solely on plastic pollution. This isn’t surprising, as unlike many other human pollutants in the environment, plastic debris is very visible and images of sea turtles with plastic cotton buds stuck up their noses and birds tangled in fishing gear is highly emotive. Indeed, plastic pollution is a massive problem and I am of course a passionate advocate for the reduction of plastic waste across our society. But I feel that we, the general public, and legislators are letting the subtle but much more dangerous environment pollutant go unchecked and it is quite literally getting away with murder right under our smog filled noses.


So what are chemical pollutants?

Firstly I think it’s important to define what a chemical is before moving on to what makes a chemical a pollutant. And while this may seem really basic to many of you, there does seem to be a few misunderstandings and misconceptions about what chemicals are and what they do, so please indulge me for a few moments (I am a scientist, so  I do love a good aul’ definition). 

A chemical is any substance consisting of matter, including any liquid, solid, or gas, and can occur naturally or be made artificially.

Natural chemicals are produced by nature without human intervention, for example, petroleum and heavy metals (e.g. copper, lead and zinc) are naturally occurring chemicals found in or under the Earth’s surface. Similarly, oxygen, nitrogen and carbon dioxide are naturally occurring gases, and together make up most of the air we breathe. The most important naturally occurring liquid chemical on earth, consisting of hydrogen and oxygen, is of course water. Synthetic chemicals on the other hand, are made by humans using different methods than those used by nature. The worldwide production and use of synthetic chemicals has increased dramatically since World War II. Today more than 100,000 man-made chemicals are used commercially around the world ranging from food preservatives/additives, pesticides, fungicides, flame retardants, dioxins, plasticisers and plastic additives, detergents, surfactants, emulsifiers and pharmaceuticals. These are used in industrial and agricultural practices as well as millions of different everyday products that we use at home such as cosmetics, clothes, cleaning products, disinfectants, textiles, food, paints, furniture, toys, medicines and electronic goods.

For many of us (myself included) the word “chemical” has been tainted with negative connotations, but I think it’s really important to stress that just because a chemical is “man-made”, “artificial” or “synthetic” does not necessarily mean it is dangerous and likewise just because a chemical is “natural” doesn’t necessarily mean it is safe. For example, vitamin C (absorbic acid) found naturally in citric fruits can be artificially produced from glucose. Similarly carbon dioxide, while a naturally occurring chemical in air, can be toxic to us if we breathe in high concentrations of it.

Problems with chemicals, both natural and synthetically derived varieties, arise when they are released into the environment where they are not naturally present or when they are present in the environment at amounts higher than their natural background values. In both case they can potentially have detrimental effects on the health of humans, plants and wildlife and/or change global geophysical systems. 


Where are chemical pollutants found?

Today, chemical pollutants are found in pretty much every environmental compartment you could think of; oceans, lakes, rivers, estuaries, forests, sediments, soils and the air we breathe. They are even detected in the internal tissues of humans and wildlife including in blood, adipose tissue, breast milk and umbilical cord samples. Chemicals pollutants are not only found in urban and industrialised hubs but also in rural areas as well as extremely remote regions of the world such as the Arctic, the Antarctic, the deep sea and the Tibetan plateau.

What are the effects of chemical pollutants?

Chemical pollutants can have both visible and invisible effects. We’ve all seen the images of sea birds covered in oil following spills and dead fish in lakes as result of extreme algal blooms, but chemical pollution can have impacts on wildlife and ourselves that aren’t always obvious. These effects are called sub-lethal effects, which basically means they don’t kill us (at least not straight away!!) but cause subtle, though by no means inconsequential, changes in the way our biological systems work. Considering there are so many chemical pollutants, all with different molecular structures and modes of action, it would be extremely difficult for me to summarise the potential health effects of them all in just a single blog post. Chemical pollutants can affect multiple biological systems, from the nervous and reproductive systems to immune and heart functions. They can also have varying effects depending on the life stage in which exposure occurs, for example developmental versus adult life stage effects. There are even differences across species, with some animal groups being particularly sensitive to one chemical and other groups more resistant. Finally, we unfortunately don’t live in a world where chemical pollutants occur in isolation, there can be hundreds of them all present in the same soil, air or water sample at the same time and the biological effect of these chemicals can change depending on what it is mixed with (known as mixture toxicology). 

The major players

While there are far too many chemical pollutants to identify here, chemicals released during the combustion of fossil fuels are one of the biggest contributors in terms of air pollution. The toxic chemicals released include particulate matter which are inhalable and respirable particles (composed of sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water) as well as ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2), polycyclic aromatic hydrocarbons (PAHs) and heavy metals (nickel, lead and copper).  Other chemical air pollutants of significance are flame retardants, polychlorinated biphenyls (used as coolants in refrigerators) and dioxins/furans (by-products of combustion processes). In terms of water pollution the most significant contributors are fertilisers, pesticides, pharmaceuticals, oil, gasoline and dyes used in the textile industry. Finally, the major soil contaminants are heavy metals (lead, copper, mercury, arsenic, nickel, zinc),  agricultural pesticides and fertilisers and PAHs.

So there you have it, a not so brief intro into the world of chemical pollutants. I can hopefully do some small articles in the future to explain a bit more about each of these chemicals. I am pretty passionate about flame retardants and their impacts on the aquatic environment so watch this space…

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