The passage discusses how the Arctic region is contaminated by pollutants from distant sources through a process called transboundary pollution. Various toxic contaminants from agriculture, industry, and nuclear incidents elsewhere in the world are carried north by atmospheric, river, and ocean currents. These pollutants accumulate in Arctic ecosystems due to the extreme cold conditions and break down more slowly. The contaminants become highly concentrated as they move up the Arctic food chain, potentially affecting human health. An international scientific monitoring program was established to study this problem.