The wintry spell cast upon Southampton and the rest of the UK courtesy of Storm Emma and the eastern Siberian winds has left the UK in meltdown. Attempts to reduce the impact of the adverse weather had been implemented earlier in the form of grit, but is this having a negative effect on the surrounding environment?
Grit is a mixture of rock salt (sodium chloride), sand, and anti-caking agents, and it has been used to treat roads in the UK since the 1960s to improve safety for drivers. Rock salt combats the elements by lowering the freezing point of water on the surface it covers, which simultaneously prevents ice from forming, and melting existing ice and snow.
Once everything thaws, what happens to the copious amounts of grit lining our roads? According to research completed at the Univeristy of York, 75%-90% of grit finds itself within 10 metres of the road. However, this is highly concentration dependent as higher amounts are able to disperse further away. When in high concentrations, grit has a detrimental effect on plants, animals and water sources. For instance, if sodium chloride mixes with soil, it alters the soil composition, causing changes to pH and ion concentrations and disrupting the biogeochemical cycle. The salt can also become dissolved in the ground water, which is subsequently transported to rivers and streams. Alternatively, some salts may directly enter water systems via road drains. This is of increasing concern as the major water supply for the UK is derived from the area which experiences the highest level of snow and so the most gritting: Britain’s uplands. The main roads of the uplands tend to follow the river courses, posing a real threat to the chemical and ecological quality of the water supply.
Animals can also be heavily affected; for example, dogs become irritated by grit on their paws, causing them to lick their paws and ingest the grit mix, which can create serious health implications. Migratory birds are also affected as seed-eaters are unable to distinguish between salt crystals and the mineral grit they require in their diet. This again poses health risks.
With mounting evidence for the negative impact of the use of grit (especially within countries that experience long bouts of snow such as Canada and the USA) science is looking for a way to provide an eco-friendly alternative. Many have been suggested such as potassium acetate, which is biodegradable and non-corrosive. Unfortunately, they are drawbacks as potassium acetate attracts moisture from the air, keeping the pavement wet and, if it contaminates a water source, it reduces oxygen levels. The biggest downfall is that all grit substitutes cost significantly more than rock salt. Therefore, they are not economically viable on a large scale. This financial difference coupled with the faults in alternatives is the deciding factor regarding which substance we use on our roads.
Fortunately, the environmental effects of grit in the UK do appear to be low and short-lived due to the limited occurrence of sub-zero temperatures and adverse weather. The UK Environment Agency state:
There are minimal short-term impacts to the ecology of watercourses, the salt intake is not prolonged enough to cause significant long-term damage.
However, perhaps this will most likely become increasingly problematic as we continue to experience more extreme temperatures as a result of climate change.