Insects are on the decline all over the globe. All factors contribute to the decline of insects, including intensive pesticide use, new diseases and habitat destruction. We are becoming more aware of the importance of heavy metal pollution, which is a negative effect on our daily lives.
These substances are everywhere. These substances are found in the Earth's crust. They are also released at low levels by weathering and volcanic activity. Human activity gives them a boost. These metals are released in many ways. They can be as dust from car brakes or as fuel for power and transportation. This all raises metal concentrations beyond their natural levels. Metallic dusts can stay in the air for many millennia once they are present.
Some of these metal compounds are vital for living organisms. However, many of them can be toxic at low levels. Although there are international guidelines that are supposed to protect us against such pollution, they are not strong enough to protect insects.
Our recent research surveyed scientific literature over the past 45 years, which focused on the most closely monitored metals arsenic (cadmium), mercury, lead, and mercury. We were able to determine the levels of these metals that are toxic to terrestrial invertebrates (mostly insects). Then, we compared the results with thresholds for metals recommended for food, water, and soil by international regulatory agencies.
Although the environmental levels should not exceed human-safe limits in any case, almost half the studies found that the natural environment contained higher levels than these limits. It is not surprising that these metals nearly always kill invertebrates at these levels. Worse, 90% of studies examining metal levels below human-safe limits found harmful effects on insects.
Furthermore, although it is obvious that contamination can harm these animals, our studies only focus on sentinel species like moths or bees. These are used to provide information on possible human harm and organisms we favoured in lab studies like Drosophila. These patterns are expected to be broad, but they only reflect a small fraction of the insect biodiversity on Earth. To mitigate these effects, it is important to have a deeper understanding.
We must act immediately. Despite many local efforts to reduce the emissions of certain metal pollutants and their emission sources, global environmental metallic pollution is still high. For example, lead was banned from petrol in 1980. However, it remains high in the environment due to the processing of metals and the use of leaded aviation fuel.
It is possible to reduce metal emissions by reducing the use of gasoline, fossil fuels and metal-based pesticides. These are all good ways to help protect our environment.
Scientists and politicians also need to reconsider guidelines regarding safe levels of metal pollution to account for non-human species. This shift in thinking occurred a few years back for widespread use of harmful pesticides during intensive agriculture in many areas of the globe.
The threat of metal pollution is not being fully understood. Recent conservation plans such as the one for a more sustainable European Union Common Agricultural Policy have not recognized its potential contribution to the decline in insect biodiversity. This needs to change.