Statistical Analysis Of Climate Change Signals In Typical Persistent Organic Pollutants Over The Arctic And The Great Lakes

Persistent organic pollutants(POPs)are refered to as natural or synthetic organic contaminants that can transport a long distance in the atmosphere and over a long period of time,accumulate in various environmental media(atmospheres,soil,water,organisms,etc.).POPs impose adverse risks to human health and the environment.POPs are carcinogenic,teratogenic and mutagenic.The lipophilicity of POPs enable these toxic chemicals to reach a higher concentration in organisms due to their bioaccumulation.POPs in the environmental medium tend to be transferred to the solid phase or lipid of organic tissue which slow down their metabolism,leading to bioamplification through human food chain.Due to their persistent in the environment,long-range transport potential,toxicity,and bioaccumulation in food chain,many POPs have been banded or restriction in use since the 1970 s worldwide.However,given thir persistence,the intensive,widespread,and historical use of POPs have resulted in their storage in the environmental reservoirs such as water,soil,vegetation,and ice,etc.These environmental reservoirs as secondary sources of POPs have become the major source of POPs emissions after their ban.Since many of the physical and chemical properties of POPs,such as vapor pressure,Henry's law constant,and phase-partiioning,are temperature-dependent,climate change featured by climate warming will inevitably affect the reemission and distribution of POPs in different environment media.The re-emission of POPs has a profound effect on POPs' environmental fate and biogeochemical cycling.However,due to the lack of continuous observation of ambient concentration of POPs for a long time,the relationships between POPs environment fate and climate change,which needs long-term sampling data of POPs atmospheric concentrations,were still not well understood,.In the past two decades,several POPs monitoring programs have been operated,noteably the long-term POPs atmospheric monitoring programs conducted in the Arctic and the Great Lakes,namely,as the Arctic Monitoring and Assessment Program(AMAP)and the Integrated Atmospheric Subsidence Network(Integrated Atmospheric Deposition Network,IADN)in the North America Great Lakes region.These two programs started operation in the early 1990 s and now the available air concentration measurement data has extended over 20 years.These two programs provide unique POPs concentration time series and can be used to study the relationships between decadel years scale climate change and POPs concentration.In the Arctic,lower temperatures promoted the partitioningof POPs from air to liquid or solid,and thus POPs were deposited in snow,ice,vegetation,and soil where prevailing cold temperatures help to preserve them and,therefore,extend their residence time in the environment.This is so called "global distillation" effect.As a result,the Arctic becomes a POPs sink in the Northern Hemisphere.The Arctic is also most susceptible to climate change in the globe.In this context,we have focussed our investigation in the Arctic region.We have also extended our study on the relationship between POPs environmental cycling and climate change in the Great Lakes region because Great Lakes region is located relatively higher latitudes where the IADN monitoring program also provides long history atmospheric monitoring data of POPs.In the present study,the linkage between POPs air concentrations and climate change was assessed by statistical analysis to identify the abrupt change point,envionmental cycling,and the "cocktail effect" of POPs data which might be associated with climate change.Firstly,we analyzed the half-lives of POPs at the four POPs monitoring sites in the Arctic and three monitoring sites in the Great Lakes region.Results showed that POP concentrations in the Arctic and the Great Lakes region exhibited declining trend since thier global ban and restriction.However,such downward trends were slowing down in the first decade of the twenty-first century,and this feature in the Arctic is more pronounced than the Great Lakes region.To enhance our understanding of the changes in the half-life and environmental cycling of POP concentrations,extensive statistical analysis was conducted to identiy statistically significant evidence in the relationship between POPs and climate change.We conducted three statistical tests for POP trends and step change(also referred to as the abrupt change or abrupt discontinuities)using POP obversation data collected at Alert,Zeppelin,Storhofdi,and Pallas sites in Arctic.Results showed that PCBs(Polychlorinated Biphenyls)and OCPs(Organochlorine Pesticides)were two substances groups showing more significant statistical abrupt change points.We identified two consecutive years of step change points in POP time series in 2001 and 2007-2008,respectively.These two step change points(2001 and 2007-2008)coincide with the years during which arctic temperature turned to positive anomaly and this positive anomaly persists thereafter.Likewise,these two step change poing years also coinside with the occurrence of the lowest sea ice extents over the past decades.The significant increases in the POP concentration anomaly in the step change point years are associated with POPs re-emission under arctic climate warming which forces the temperature rise and sea ice melt.We suggested that the association between POP environmental fate and climate change would become more evident after the "turning point"(step change)in POP concentration time series.To further establish the connection between climate change and POP concentrations,we extends the two-dimensional POP concentration time series data into three-dimensional data by statitical seperation,including time,period,and period intensity via wavelet analysis which examined the common cycle range and the connection between POPs observations data and climate index.Results showed that there was a close relationship between the selected climate index and POP concentration data in the period 18-84 months.The seasonal variation of POPs in the Great Lakes region was stronger than that in the Arctic.The significant correlations were found among the wavelet intensity of the six POPs at the three monitoring sites in the Great Lakes.This correlation may reflect the difference among POP time series at different observation sites caused by climate change.The long-term trend of POPs and the changes in concentration time series in 18-84 months period was observed by Kolmogorov-Zurbenko(KZ)filter.Although the long-term trend indicated that the decreasing trend of ?-HCH(Hexachlorocyclohexane)and ?-HCH was stable,the results of the wavelet analysis still showed the turning point for POP concentrations time series.The changes in POPs concentration time series measured in the Arctic the Great Lakes are associated not only with climate change,but also with their degradation in multiple environments,seasonal changes,and other unknown factors.In this sense,the problem to discern the causes for the changes in POP measurement data can be regarded as a blind source signal separation problem.Isolating these unknown factors from POPs observations may lay on the solution of the "cocktail party effect".To solve this problem,the Independent Component Analysis(ICA)model was used in our investigation which is a major method to solve the "cocktail parth effect".Compared with selected climate index and major signals extracted from HCB and PCB52 measured data in the Great Lakes,we found that the typical signals of HCB and PCB52 were characterized by seasonal and interannual variability.We identified that the signal(signal 2)extracted from monitored ?-HCH data at the three arctic sites was a typical signal indicating the long term trend of this toxic substance.The decline trend of signal 2 is much stronger than the decline trend of ?-HCH concentration data at each site(Alert,Storhofdi and Zeppelin)in the Arctic.Since signal 2 excludes the seasonal changes,the results indicate that seasonal variation is also an important factor in mitigating the degradation of POPs.In addition,through the analysis of the cocktail party effect in various POP data time series,we found that the "cocktail party effect" in POPs monitoring data was site dependent.Our results suggested that the relationship between observed POP concentrations and climate change might be more evident in thoses regions where POP time series was of weaker seasonal change and ecologically sensitivity to POPs contamination.It is also recommended that those POPs whose physical and chemical properties have stronger response to the evolution of environmental facotrs should be selected to detect the linkage between the climate change and POPs concentration.