Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE credits
Persistent organic pollutants (POPs) present a class of substances which are of high concern due to their toxicity and ecotoxicity, long-range atmospheric transport and resistance to degradation. A combination of analytical measurement and modeling researchis a powerful means for understanding chemical fate and behavior. Among all availablemodeling approaches, multi-compartmental fugacity modeling is a common and relatively simpleway to simulate the concentrations and distributions of pollutants. This approach isalso applied hereto study a well-studiedgroup of POPs –polychlorinated biphenyls (PCBs).
Climate changeis potentially one of the largest global environmental problems facing society today. Climate change resulting from anthropogenic activities may impact the transport, fate and exposure of POPs due to alterations in climatic and landscape properties (e.g. temperature, windspeed, precipitation etc.). Modeling studies have previously been carried out to investigate their influence on POPs fate under defined scenarios.However, in previous work the uncertainty of chemical properties has not been considered. We hypothesize that the uncertainties in physical-chemical parameters could actually cause a greater impact predicted concentrations than variability in climate parameters such as temperature, wind speed and precipitation.
To test the hypothesis, a 4-compartment Level III fugacity model –ChemCAN spreadsheet model is used. A combination of8 climate variables, 3 physical-chemical properties and 4 degradation properties are chosen to investigate how the variability and uncertainty affect the environmental fate of 6 selected PCBs congeners. In total, 18 forecasts are createdin the investigation and outputs provided forconcentrations, distributions, total amounts, long-range transport potential indicators and persistence of the chemicals. We arbitrarily model the Japan region for which we had environmental parameterization in the ChemCAN model. Monte-Carlo simulations areundertakenusing the
Crystal Ball®computer software to perform correlation and sensitivity analyses, in order to specifically examine andcompare the influence brought from variability and uncertainty.Datafor climate variablesarecollected and calculated from Intergovernmental Panel on Climate Change –Data Distribution Centre (IPCC-DDC), while thosefor chemical propertyuncertainty arecollected and calculated from literature sources/methods.
The results are interpreted focusing on the two types of analyses –correlation and sensitivity. Within the correlation analysis between climate variables and PCB fate predictions, temperature is the most important factor affecting total amount, concentrations and distributions, especially in the atmosphere compartment. It alsoinfluencesthefugacity of the PCBs in each media, as well asthe reactive residence times. The uncertainty of temperature increases resulting fromclimate change has more influence thanvariability in mean temperature however. Precipitation hardly has any influence onPCB fate,althoughthe change in precipitationdue to climate changecould affect distributions in surface water and surface soil for light chlorinated PCBs congeners due to the extremely high coefficient of variation. Wind speedalso has little impact onpredictions other than for long-range transport potential descriptors, namely characteristic transport distance and transfer efficiency. Wind speed also affectsthe advective residence timein theair compartment forPCBs.Within the correlation analysis between properties and PCB fate predictions, all the chosen 3 physical-chemical properties, vapor pressure, water solubility and water-octanol partition coefficient, significantly affect the predictions. Vapor pressure has more influence onpredictions related to air and more significantly on lighter PCBs, while water solubility and the water-octanol partition coefficient mostly affect the heavier PCBs, especially
MSc. Thesis in Environmental Chemistry
the predicted outcomes in water and sediment. Despite a fairly small uncertainty inphysical-chemical propertiescompared to many other chemicals, the influence on PCB fate is noticeable. Degradation properties, which have a rather high uncertainty, also significantly affect PCB environmental fate and degradation half-lives in air and soil have much more significant influence than those in water and sediment.
In the sensitivity analysis, variability and uncertainty are assembled into a single simulation. When excluding degradation properties, it could be concluded that uncertainty inphysical-chemical properties is usually dominant forPCBs. One notable exception isthat precipitation change has a greaterinfluence on PCB-8, which is also the lightestincluded inthe study. If degradation propertiesare included, degradation half-lives in air and soil are always the dominantsource of uncertainty to predictions.
The main conclusion of this thesis is that the uncertainty in chemical property datais generally more important than variability in climate parameters in controlling variance in predicted environmental concentrations.This supports the hypothesis of that was raised at the beginning of this study.
2011. , 66 p.