Kevin A. Johnson

Seasonal bioavailability of sediment-associated heavy metals along the Mississippi river floodplain.

A value of simultaneously extracted metal to acid-volatile sulfide (SEM-AVS) can provide important information regarding metal availability in anaerobic sediment. SEM and AVS concentrations were obtained by the cold-acid purge-and-trap technique during spring and summer at six locations along the Mississippi River floodplain. SEM-AVS values and AVS concentrations did not vary significantly between locations during both seasons. AVS concentrations were significantly greater during summer than spring, resulting in significantly lower SEM-AVS values in summer. Total SEM concentrations did not significantly vary between seasons or specific locations. SEM-AVS values were greater than one at each location during both seasons. Sediment metal toxicity was predicted to be absent for benthic organisms along the river floodplain.

Partitioning of chlorpyrifos between water and an aquatic macrophyte (Elodea densa)

Abstract Chlorpyrifos is a widely used organophosphate (OP) insecticide. As such, the potential for off-site migration exists. This research was conducted to determine the ability of plant material ( Elodea densa ) to accumulate chlorpyrifos from the water column. Our system consisted of one hundred Elodea densa stems in a 38 L glass tank in moderately-hard water (80g CaCO 3 /L H 2 O). Water and plant samples were collected prior to fortification and in intervals from 1 hour to 14 days after onset of the experiment. Chlorpyrifos was shown to dissipate over a 2-week period in the aqueous phase and accumulate in Elodea densa . From our studies, it is apparent that these aquatic macrophytes have the ability to sorb organic compounds, such as chlorpyrifos, and assist in removing them from the aqueous environment.

Passive sampling devices for rapid determination of soil contaminant distributions

The effective remediation of contaminated waste sites requires accurate identification of chemical distributions. A rapid sampling method using passive sampling devices (PSDs) for soil contaminant characterization can provide a more thorough site assessment. We evaluated a PSD to estimate polychlorinated biphenyl (PCB) levels in contaminated soils in both laboratory and field studies. PSD sampling increased with soil analyte concentration and decreased moisture content. For PSD calibration, we compared PCB concentrations in 36 PSDs and 18 soil samples. PSD uptake and soil concentration demonstrated a linear relationship with an r2 value of 0.86 and a slope of 0.88. PSD concentrations were then used to predict soil contaminant distributions at a hazardous waste site. Predicted soil concentrations ranged from 0.01 to 200 ppm as total aroclor 1254.

Placental 11β-Hydroxysteroid dehydrogenase type 2 expression: Correlations with birth weight and placental metal concentrations.

INTRODUCTION Infants born below 2500 g are classified as low birth weight. Excess in utero exposure to cortisol has been linked to restricted fetal growth. Placental production of 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) inactivates cortisol before passage into the fetus. The present study tested the hypothesis that placental 11β-HSD2 expression is positively correlated with an individualized birth weight centile and raw birth weight, and examines the relationship between metal concentrations in placental tissue and 11β-HSD2 expression. METHODS Placentae from 191 births were collected and samples preserved to maintain mRNA profile. Placental 11β-HSD2 expression was measured via qRT-PCR. Addition samples were collected from placental tissues and uniformly dried in order to quantify 18 metals via ICP-MS (n = 160). RESULTS A significant, positive correlation between 11β-HSD2 expression and individualized birth weight centile (p = 0.0321) and birth weight (p = 0.0243) was found. Additionally, maternal age and gestational age were positivity correlated with each other (p = 0.0321). Birth weight was significantly different with race, marital status, education and maternal tobacco use. Four metals (Co, Mn, Ni, Zn) demonstrated significant positive correlations (p < 0.05) with 11β-HSD2 expression. Sex specific differences were found; Co, Cu, Fe, Zn, and Ni were positively correlated with 11β-HSD2 expression in males only, no significant correlations were found in the female only sample. CONCLUSION These data indicate that the growth potential of a fetus is related to the 11β-HSD2 expression in the placenta, and that 11β-HSD2 expression is related to the trace metals status of the mother.

Assessment of solid phase microfiber extraction fibers for the monitoring of volatile organoarsinicals emitted from a plant-soil system.

Phytoremediation, the use of plants and microbes to clean up inorganic and organic pollutants, has shown great promise as an inexpensive and feasible form of remediation. More recently, studies have shown that some plants have an amazing capacity to volatilize contaminants and can be an effective remediation strategy if the chemicals released are non-toxic. Arsenic contamination and remediation has drawn great attention in the scientific community. However, its toxicity also varies depending on its form. We evaluated, optimized, and then utilized a solid phase microfiber extraction (SPME) head space sampling technique to characterize the organoarsinical emissions from rabbitfoot grass (Polypogon monspeliensis) in arsenic treated soils to determine if the potentially more toxic organic forms of arsenic (AsH3, AsH2CH3, AsH(CH3)2, and As(CH3)3) were being emitted from the plant-soil system. The SPME fiber that proved best fitted for this application was the DVB/CAR/PDMS fiber with a 45 min sampling period. We did detect and confirm the emissions of dimethylchloroarsine (AsCl(CH3)2) and pentamethylarsine (As(CH3)5). However, it was determined that the more toxic organic forms of arsenic were not released during phytovolatilization.

Passive sampling devices as surrogates for evaluating bio availability of aged chemicals in soil

The fraction of a chemical available to soil‐dwelling organisms such as earthworms is not simply related to the concentration of that chemical in the soil determined through rigorous extraction methods. Aging is one of the processes that are known to affect exposure of chemicals to organisms by decreasing the available fraction in soil with time. Passive sampling devices (PSDs) are potentially direct chemical indicators for assessing bioavailability of hydrophobic pesticides (and other chemicals) in soil. In this study, a pesticide mixture (six organochlorine pesticides including aldrin, dieldrin, endrin, lindane, heptachlor, and p,p‘‐DDT) was aged in two types of soil (sandy loam and silt loam). Uptake rates and maximum concentrations of the chemicals in earthworms and PSDs placed into the soils were determined over 36 days. There was a general trend towards decreased chemical uptake in the aged soil and in the soil with higher organic carbon content (both initial uptake rates and maximum concentrations)...