Pim1 Sheila MacIntyre Chem. 505 Dr. Hermanson/Leslie Anderson. Abstract

Transcription

1 Pim1 Sheila MacIntyre Chem. 505 Dr. Hermanson/Leslie Anderson Abstract Introduction The purpose of this assignment is to estimate the enthalpy of vaporization, H vap of a semi volatile industrial compound, 2,4,4 -trichlorobiphenyl 28 (Figure 1) using the Clausius-Clapeyron equation. Polychlorinated biphenyls (PCBs) are a group of semi volatile chemicals that contain 209 individual compounds or congeners with varying harmful effects. PCBs made in the United States were marketed under the trade name Recolor. Before 1974, PCBs were used in capacitors, transformers, plasticizers, surface coatings, inks adhesives, pesticide extenders and carbonless duplicating paper. (1) PCBs are no longer used or produced in the United States; the major source of exposure is the redistribution that is already present in the soil and water. PCBs are still detected in soil and sediments and slowly release into the water sources over time. Due to the environmental recycling of the compound and bioaccumulation through the food chain there is a concern of the toxicity to humans and the environment. Chronic long term exposure to some PCBs by inhalation in humans have resulted in respiratory tract symptoms, gastrointestinal effects, liver effects, skin rashes and eye irritation. Studies have indicated an association between dietary exposure and developmental effects. Animal studies have reported an increase in liver tumors and human studies have provided evidence of an association between PCBs exposure and cancer. (1) PCB 28 has been used as a pesticide in Dexter, Michigan, which is one of the apple producing states in the United States (2). The purpose of this paper is to evaluate the concentration of the gas phase of the PCB 28 and if there is a correlation to temperature. Figure 1. 2,4,4 -trichlorobiphenyl 28 (3) MM= gmol -1 Water solubility=0.27 mg/l 25ºC Henry s Law Constant = atm-m 3 /mole Experimental section and Data Analysis

2 The data was collected by Hermanson et. al., from Dexter, MI covering the period of May 1992-February Field sampling methods and sample analysis are presented in this paper. (2) The PCB mixtures found in environmental media (air, waste, sediments, and food) will differ in composition from the commercial mixtures due to differential partitioning, biotransformation, and bioaccumulation among the individual compounds. (1) The enthalpy of vaporization H vap is use to determine the movement of semi volatile compounds into and out of the atmosphere. (2) The H vap tells us how much energy must be applied to put the substance into the gas phase. The value of can be H vap estimated by using the Clausius-Clapeyron (CC) equation (2): LnP= (- H vap / R) T-1 + I P= partial pressure in atm or Pa R= gas constant T= temperature (K) I= constant (y-intercept) The concentration of PCB 28 was expressed in ng m-3 and required a conversion of the values to pg m-3, and then to moles L-1. The data was then converted to partial pressure using the ideal gas law. (2) The temperature values were converted to Kelvin. The conversion of pressure stated in atm is: (2) P= (C/MM) RT(10-15) C=concentration (pg m-3) MM = molecular mass (g/mol) R = gas constant ( L atm K-1 mol-1) T = temperature (K) P = partial pressure (atm) For the data the Ln of partial pressure was plotted against 1000 T-1 in order to identify the temperature related trends of particle/gas distribution. (2) To solve for H vap, the slope from the regression line of the (CC) equation and multiplied by R ( J K-1 mol-1).

3 Results and discussion The (CC) equation was applied and the statistical results of the regression for PCB 28 that was analyzed in Excel is in Table 1a.. The graph for the data is in Figure 2. Table 1a. Regression Analysis for PCB 28 SUMMARY OUTPUT Regression Statistics Multiple R R Square Adjusted R Square Standard Error Observations 61 ANOVA df SS MS F Significanc e F Regression E-11 Residual Total Coefficients Standard Error t Stat P-value Lower 95% Upper 95% Lower 95.0% Intercept E X Variable E

4 Figure 2. Concentration of PCB vs. Temperature 1000T-1 vs. LnP Ln P cogener 28/31 Linear (cogener y = x R 2 = T -1 (K) Conclusion The results show that the relationship are strong for PCB 28 at Dexter (r = 0.73) and significant (p < 0.05) and the F value > F significance. The H vap = 43 kjmol-1, this is the energy put into PCB 28 into the gas phase. When these compounds are moved into the gas phase from a liquid, energy is applied in the form of insolation or simply warmer air. Once in the gas phase, these compounds move where the winds take them. When they encounter cooler air, they may condense by losing the amount of energy that had been applied. (2) There is no indication that there is a local source of contamination. When H vap is a large value >50 is where the source of contaminant is local, because there will be a high local concentrations of the contaminant in summer and low concentrations is winter. (2) Since the value of delta H is not very small, it is considered that local temperature changes are influencing contaminant concentrations and that the contaminants are being transported from somewhere else possibly near by. References 1. Agency for Toxic Substance and Disease Registry (ATSDR). Toxicological Profile for Polychlorinated Biphenyls. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA Hermanson, M. H., D.J. Moss, C.L. Monosmith, and G.J. Keeler (2007), Spatial and temporal trends of gas and particle phase atmospheric DDT and metabolites in Michigan: Evidence of long-term persistence and atmospheric emission in a high-ddt-use fruit orchard, J. Geophys. Res, 112, D04301, doi: /2006jd

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