Environmental contaminants are emitted un-/intentionally. Pesticides are a classic example of intentional release of a toxic chemical to the environment. Other chemicals are released unintentionally to the environment e.g. by-products from industries. Furthermore, contamination from historical use may still be a source of emissions, e.g. via contaminated sediments and land.
The further fate of the contaminant depends both on properties of the substance and to which media the emissions took place. Some chemicals are long-lived as they persist degradation. Such chemicals can be transported long distances in air and water, accumulate in food webs and pollute areas and animals far from the original source.
Transport of POPs can be illustrated by “global fractionation”. They evaporate from the source – e.g. pesticides used in a southern agriculture. The pesticides are then transported with air further north (in the northern hemisphere), precipitate/scavenges out from the air. Eventually, the POPs repeat this process in several steps (“grasshopping”) until they reach the Arctic (Wania and Mackay 1996).
Past, current and future emission patterns of contaminants
Emissions of legacy POPs such as DDTs, PCBs and HCHs have decreased during the last decades due to extensive regulatory action, including complete ban in several countries. Metal emissions, such as mercury, are also expected to decrease.
However, Pacyna et al. (2010) estimated an increase of Asian mercury emissions unless emission controls will be implemented. This is of high importance in a global perspective, since the emissions in Asia are estimated to be higher than any of the other continents. If emissions will continue to increase largely depend on economic development and advances in industrial techniques and emission control techniques. For the metals and unintentionally formed POPs, such as the dioxins, a complete ban is not possible as the contaminants are naturally occurring and unintentionally generated in processes not aiming to emit these contaminants.
As permafrost thaws in the Arctic, waste sites may leak contaminants to the receiving water systems. Less ice cover in Arctic facilitates shipping and off shore activities in a vulnerable area, where sea charts and search & rescue systems not always are well developed/within acceptable reach. These factors need to be taken into account for future work with contaminant risks in the Arctic, especially environmental pollutants related to transport, oil and gas. The North West and North East passage have already been used for shipping traffic. Shipping and offshore in the Arctic was one of the themes at the Arctic Frontiers 2014 conference in Tromsø, Norway.
Pathways and long-range transport of pollutants
POPs and mercury reach the Arctic mainly via atmospheric long range transport. Some substances are also transported via ocean currents and rivers.
DDT and PCB are examples of atmospheric transported compounds, while α-HCH can also be transported by water currents. Atmospheric transport of semivolatile POPs to the Arctic takes place via repeated evaporation and deposition events, resulting in the pollutant “hopping” to its final destination in the Arctic (Wania and Mackay 1996). Mercury is also transported from lower latitudes to the Arctic via the atmosphere. The transport mechanism involves different forms of mercury, both gaseous elemental mercury (Hg(0)), Hg(II) and particle bound species, and involve an oxidation process.