Pollution risks could rise as climate changes
16 April 2009, by Tom Marshall
Dust storms, agricultural chemicals and harmful bacteria from British farms are likely to pose a growing threat to human health because of climate change, according to new research.
The authors of the paper, which appears in Environmental Health Perspectives, say policy-makers need to start thinking about these risks and how they can be managed.
They also argue we need far more research into the threat different pollutants will pose to human health as the climate changes.
The paper focuses on Britain's farming sector, and identifies areas in which climate change will affect the dangers people face from harmful chemicals and microbes. While there are a few bright spots, in general its conclusions aren't encouraging. 'We anticipate that climate change will result in an increase of risks of pathogens and chemicals from agriculture to human health,' the authors write.
'It's definitely an area policy-makers and research funders need to be looking at,' says Dr Alistair Boxall, an environmental chemist at the University of York and the paper's lead author. 'One of the key messages here is how complicated this subject is - initially we were hoping to make firm predictions of what impact climate change would have on human health, but we soon realised that a lot more interdisciplinary work is needed before we will be in a position to do this,' he adds.
Boxall explains that it's not certain where the greatest risks to our health will come from - not only do we not know just how harmful many pollutants are, but we don't know which of numerous possible climate change scenarios will become a reality. Because of this, the research tries to explore possibilities that we need to bear in mind rather than making firm predictions.
Blowing in the wind
One major area of concern is that hotter, drier summers could damage soil structure and cause more dust to be thrown up from the land during tilling or harvesting, and that this dust, blown on the wind, could carry diseases and poisons into contact with humans.
Soil erosion and dust storms are becoming more of a problem for large agricultural producers like China and the US; similar problems could start to affect Britain. Indeed, some British farmers are reporting that summers are much dustier now than when they were young. 'This aspect of our research has met with lots of interest in the US, where they have a major problem with huge dust storms,' says Boxall.
Another potential problem is that farmers may need to use more pesticides, if warmer temperatures lead to more insect pests. This would mean people could be exposed to more pesticide residues on fruit and vegetables, as well as in food from fish and livestock which have absorbed more chemicals through the food chain. Higher levels of windblown dust could transport pollutants further than at present, worsening the problem.
But exactly how pesticides affect human health, and how this would change if we were exposed to larger quantities, is hardly a settled topic.
For example some scientists claim that pesticide exposure can cause Parkinson's disease; other researchers disagree vehemently. Other studies have suggested that regular exposure to chemicals makes farm workers more vulnerable to certain cancers, though again this conclusion is not universally accepted.
North American studies have suggested exposure to certain herbicides can lead to problems ranging from circulatory and respiratory problems to changes in the ratio of male to female offspring. Other recent research has highlighted the potential dangers of agricultural antibiotics causing microbes in the soil to become more drug-resistant.
Chemicals and heavy metals in the environment aren't the only problem; pathogens like e coli or salmonella could be equally harmful and in many cases their effects are better understood. Unwelcome bacteria may breed more quickly in a hotter environment, although they may also die more quickly in very dry conditions.
Though summers are in general expected to be warmer and drier, bursts of extreme rain are also predicted to get more common; this could increase problems of polluted runoff from farmland into streams and rivers.
These effects may not be confined to newly-created pollution; heavy rainfall may also disturb previously-buried layers of pollutants from the past. Conversely, during dry periods rivers levels will tend to be lower, meaning that any pollution entering them makes up a bigger proportion of the total flow and potentially increasing the risk to humans.
The range of potential risks is wide, and there could be several indirect effects of a changing climate and human responses to it. For example many councils are trying to compost more municipal waste to lower their reliance on landfill; if the resulting compost ends up on farmland, more pathogens and pollutants may end up in agricultural land and ultimately in our food.
Boxall says much more research is needed, both in gathering data about the effects of these pollutants on humans and in modelling how they come into contact with humans. In some cases we could look at other nations whose present climate resembles the climate predicted for the UK in the future.
But he argues that the problems should be manageable if we make sensible preparations. 'We should begin to introduce more strategic monitoring programmes to find out how things are changing. And we need to develop scientific understanding of the exposure pathways we don't face much at the moment.'
He gives the example of flooding; despite recent high-profile incidents in Britain, floods are still comparatively rare and our understanding of the risks is probably weaker than in other areas such as pollutant runoff from fields, which have been recognised as problems in Britain for longer.
In many cases measures to deal with potential problems, such as better filtration technologies for drinking water, are already available, though installing them will be costly. In others, measures are being developed that could help at little extra cost.
For example, Canadian researchers have been looking at ways of limiting the creation of dust by changes in the way fields are planted and drained - one idea is that before the land has time to dry out in hot weather, a farmer could block off drainage ditches to keep water in the soil as long as possible.
The research comes out of the Environment and Human Health (EHH) programme, a multidisciplinary initiative intended to research how a changing environment will affect human health and how
EHH is supported by the Biotechnology and Biological Sciences Research Council, Defra, the Economic and Social Research Council, the Engineering and Physical Sciences Research Council, the Environment Agency, the Health Protection Agency, the Ministry of Defence, the Medical Research Council, the Natural Environment Research Council and the Wellcome Trust.
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