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Friday 31 May 2019

Toxic Climate: how climate change changes pollution

When it comes to climate change, contaminated land is the forgotten risk.

Climate change leaves us worrying about quite a lot of things: tropical diseases, extreme weather events, extinctions... But we don’t tend to worry about pollution outbreaks. In DEFRA’s climate change risk assessment, it doesn’t even get a mention.

But is that because we’ve forgotten the risks, or because we don’t know?

Extreme weather may affect land safety, access and use. Image © Rowena Fletcher-Wood

Lots of land is “contaminated land”. This doesn’t mean it glows yellow in the dark or is a breeding site for mutant flesh-eating bacteria. Most land is contaminated by waste from agriculture, industry, energy or medicine, and that can be anything from fertilisers that cause algal overgrowths to pharmaceuticals that make male fish feminine[1]. Humans like to concentrate chemicals to put them to use doing specific jobs. This is great when they’re where they’re supposed to be, but leftover chemicals or waste products are still relatively concentrated and can be poisonous or harmful.

Contaminants can also come from the land itself: like arsenic, which is rife in various rocks. Or radon, a radioactive gas found in granite, and especially Cornwall.

There are three main ways of dealing with chemicals in the environment:

1. Spread them out – diluting them more and more until they’re no longer at harmful concentrations
2. Concentrate them – and lock them up in a box or a landfill somewhere they can’t do any harm
Or 3. Change them. Chemical reactions can change the nature of some chemicals, such as pharmaceuticals, making potentially harmful things into harmless things.

These processes are called remediation.

There are lots of ways of containing or remediating contaminants, but climate change could change all that. Image © Rowena Fletcher-Wood

But climate change changes everything.


Well, because of those extreme weather events we talked about earlier.

No longer can we simply look at a bit of land and go oh, there’s lots of basalt in this area, we better watch the arsenic levels, or ooh, it’s densely populated, we’ll monitor lead pollution. Things like droughts, landslides, high winds, heat waves, floods and erosion mobilise contaminants. So do changing land use, mining and industry, but those factors are controllable. The weather isn’t. And as the weather gets more forceful and unpredictable, contaminants get more difficult to contain.

Travelling contaminants can mean more unusable farmland, more unbuildable land, more human health effects and more environmental damage. Chemical reactions happen as the contaminants get to new places and meet new things – and this affects how dangerous they are: the chemical form of contaminants determines their bioaccessibility – how easily they get into plants and animals. Soil pH will also affect their chemical form and solubilities. So a contaminant may be harmless on a beach, but a bit of a cow when in a field.

So what sort of contaminants are we talking about? Heavy metals and persistent organic pollutants (POPs) like DDT are two main culprits. The problem is new pharmaceutical or industrial chemicals are being identified as pollutants every day. Just look at neonicotinoids – we used to think those were safe, then it transpired they messed up bees. This means scientists have to be ready to monitor new things, as there continue to be unexpected surprises.

Scientists also want to know when a contaminant arrives and how long it’s planning on staying around. This matters because sometimes there’s a lag between a contaminant arriving, and doing it’s dirtiest, e.g. lead poisoning. In one study on human behaviour in New Orleans, researchers found a 22 year lag between lead contamination of the air and a spike in aggravated assaults[2]. This is complicated by hydrology. Water is the main transporter of contaminants. And it moves where we can’t see it – beneath the surface of the earth. Unsurprisingly, research on this groundwater lags behind that of surface water. Plus, to properly understand it, you need concurrent knowledge of rocks and permeability. There are few experts in both, and industrists don’t tend to collaborate, leading to lots of guess work. Where is the water, what is it carrying, and where is it going next? We don’t know.

Another focus for science is modelling. Climate scientists spend a lot of their time coming up with computer models to try to guess how CO2 volumes might change, how this might affect warming, how this might affect weather, and how this might affect contaminants. But that’s many layers of speculation, and the truth is things could vary enormously with just a few small differences from the model. The butterfly effect. CO2 isn’t the only greenhouse gas, and climate change will affect different regions around the world differently, depending on factors such as latitude, elevation, and exposure. This means that overall there is too much uncertainty, not only about how climate change will affect contaminated land, but also how bad climate change will be, and what events will take place.

Scientists don’t really know how to assess our carbon footprint, especially in the future. Image © Kevin Meehan

Extreme weather may affect land safety, access and use. It invalidates our safety assessments and changes what we can and can’t do with land. It could also lead to a bun fight over culpability (who pays to fix the problem) – most current safety assessment contain the caveat that they’re based on current conditions. There’s little guidance available and the level of uncertainty is so large that most consultants don’t build climate change into their risk assessments at all. Specialists argue that climate change calls for flexible risk assessments of contaminated land and ever-evolving, best practices based on “living” documents. This could change not only how we think about contaminated land, but also risk, the climate, and scientific practice.

why don't all references have links?

[1] Jobling, Susan, et al. Widespread sexual disruption in wild fish. Environmental science & technology 32.17 (1998): 2498-2506.
[2] The urban rise and fall of air lead (Pb) and the latent surge and retreat of societal violence. Mielke HW, Zahran S, Environ Int. 2012 Aug;43:48-55. doi: 10.1016/j.envint.2012.03.005. Epub 2012 Apr 6.

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