Comparing the effects of weathering and microbial degradation on gasoline using principal components analysis

Ignitable liquid residues recovered from a fire scene will often show signs of weathering as a result of exposure to the heat of the fire. In addition, when the substrate is rich in organic matter, both weathering and microbial degradation may be observed. In this study, 20 μL aliquots of fresh gasoline samples were intentionally weathered and also subjected to microbial degradation in potting soil. These samples were then analyzed using a passive adsorption-elution recovery method and gas chromatography/mass spectrometry. Peak areas from compounds of interest were normalized and autoscaled and then subjected to principal components analysis. This analysis showed that while lower boiling compounds are subject to weathering, a different set of compounds are subject to microbial degradation. Of the compounds studied, heptane, octane, toluene, and ethylbenzene were the most vulnerable to both weathering and microbial degradation. In contrast, 1,3,5-trimethylbenzene and 2-ethyltoluene were the most resistant to both phenomena.     

Direct and Indirect Effects of Childhood Adversity on Depressive Symptoms in Young Adults

While researchers have provided evidence that recent stressors in adulthood and single traumatic events in childhood predict psychological disorder, few have examined the cumulative impact of childhood adversity on later well-being. Using a sample of 649 college students from New England, this research examines whether cumulative trauma in childhood and adolescence is related to depressive symptoms in young adults, and explores the mediating factors that operate in this association. Results indicate clear differences in cumulative trauma by sociodemographic characteristics, with males, nonwhites, and those with less than college-educated parents, reporting significantly greater levels of adversity. We also find that higher trauma is associated with both early onset of depressive disorder and later depressive symptoms. Path analyses reveal that, while some of the association between childhood adversity and depression in young adults is direct, most is explained by the mediating effects of later stress, low self-esteem, and early onset of disorder.