Agricultural Chemicals in the Alluvial Aquifer of a Typical County of the Arkansas Delta

Statistical methods and a Geographic Information System (GIS) were used to investigate potential indicators of ground water vulnerability to agricultural chemical contamination in a representative area of the Mississippi River alluvial aquifer. A total of 47 wells were sampled for analysis of nitrate, phosphorus, potassium, and 13 pesticides commonly-used in the area. Ten soil and hydrogeologic variables and five ground water vulnerability indices were examined to explain the variations of chemical concentrations. The results showed that no individual soil or hydrogeologic variables or their linear combinations could explain more than 25% of the variation of the chemical concentrations. A quadratic response surface model with the values of confining unit thickness, slope, soil permeability, depth to ground water, and recharge rate accounted for 62% of the variation of nitrate, 43% of P, and 83% of K, suggesting that the interactions among soil and hydrogeologic variables were significant. Observed trends of decreasing nitrate and P concentrations with increasing well depth and/or depth to ground water seemed to correlate with carbonate equilibrium in the aquifer and more reduced environment with depth. In view of uncertainties involved, it was recognized that the limitations associated with input data resolution used in GIS and the formulation of leaching indices limited their use for predicting ground water vulnerability. Misuse of pesticides could be another factor that would complicate the relationships between pesticide concentrations and the vulnerability indices.     

Particle Surface Hydrophobicity and the Dechlorination of Chloro-Compounds by Iron Sulfides

Halogenated aliphatic compounds (HACs) can be reduced by iron sulfides in aqueous systems. Generally, the thermodynamics and kinetics of dehalogenation reactions are controlled by the mineralogical and particle surface characteristics of the iron sulfide, the composition of the HAC and reaction conditions such as component concentrations, pH and Eh. In this theoretical and experimental investigation of CCl₄ and C₂Cl₆ reduction by FeS and FeS₂, the roles of hydrophobic and hydrophilic sites on the iron sulfides were analyzed. Experimental data obtained through zeta potential measurements, were used along with the Gouy-Chapman model and the simple two-layer surface complexation model to relate iron sulfide surface hydroxyl densities to the degree of HAC dehalogenation. The surface hydroxyl site densities of FeS and FeS₂ were found to be 0.11 sites/nm² and 0.21 sites/nm², respectively. During the dehalogenation reaction process, CCl₄ was found to decrease to its first intermediate product CHCl₃ within the first 20 hours followed by a slower process of conversion to CH₂Cl₂. The results also show that FeS is less hydrated (more hydrophobic) than FeS₂. For CCl₄ and C₂Cl₆, FeS is a better dehalogenator than FeS₂. These results imply that particle surface hydrophobicity is a critical factor in surface-mediated dehalogenation of chlorinated compounds.     

Lead levels in Chromolaena odorata (Compositae) along rural and urban roads in Akwa Ibom State, Nigeria

ＩｎｔｒｏｄｕｃｔｉｏｎＣｈｒｏｍｏｌａｅｎａｏｄｏｒａｔａ（Ｅｕｐａｔｏｒｉｕｍｏｄｏｒａｔｕｍ），ｃｏｍｍｏｎｌｙｃａｌｌｅｄ“ｓｉａｍｗｅｅｄ”ｗａｓｉｎｔｒｏｄｕｃｅｄｉｎｔｏＮｉｇｅｒｉａａｂｏｕｔ３０ｙｅａｒｓａｇｏ．Ｉｔｉｓａｓｔｒｏｎｇｌｙｓｃｅｎｔｅｄ，ｄｉｆｆｕｓｅ，ａｎｄｒａｐｉｄｌｙｇｒｏｗｉｎｇｈｅｒｂｔｈａｔｃａｎａｔｔａｉｎａｈｅｉｇｈｔｏｆ３－０ｍｅｔｅｒｓｏｒｍｏｒｅ．Ｉｔｉｓｌｏｃａｌｌｙｃａｌｌｅｄ“ｏｗｏｔｏｗｏ”ｂｅｃａｕｓｅａｔｉｔｓｄｅｂｕｔｉｔｗａ…     

Medium composition affects the degree and pattern of cadmium inhibition of naphthalene biodegradation

Metals have been reported to inhibit organic pollutant biodegradation; however, widely varying degrees and patterns of inhibition have been reported. To investigate the roles of medium composition and metal bioavailability on these different degrees and patterns of inhibition, we assessed the impact of cadmium on naphthalene biodegradation by a newly isolated strain of Comamonas testosteroni in three chemically-defined minimal salts media (MSM): Tris-buffered MSM, PIPES-buffered MSM, and Bushnell-Haas medium. Cadmium (total concentrations of 100 and 500 microM) inhibited biodegradation in each medium. Degrees of inhibition were different in each medium. Cadmium was most inhibitory in PIPES-buffered MSM and least inhibitory in Bushnell-Haas. For example, in Bushnell-Haas medium, 100 microM cadmium reduced the cell yield more than 4-fold compared to controls not containing cadmium. The same concentration of cadmium completely inhibited growth in PIPES-buffered MSM. No difference in inhibition was observed in any medium when cadmium was added 24 h before inoculation rather than when added within one minute of inoculation. Two patterns of inhibition were observed. Inhibition occurred in a dose dependent pattern in Tris- and PIPES-buffered MSM and in a non-dose dependent pattern in Bushnell-Haas. Specifically, in Bushnell-Haas, 100 microM total cadmium extended the lag phase by 23+/-8.66 h, whereas 500 microM did not extend the lag phase. Soluble, ionic cadmium (Cd2+) concentrations were measured and modeled in each medium to assess cadmium bioavailability. In media containing 500 microM total cadmium, bioavailability was highest in Tris- and PIPES-buffered MSM and lowest in Bushnell-Haas. In Bushnell-Haas, cadmium bioavailability was initially higher in the 500 microM treatments (196+/-21.2 microM) than in the 100 microM treatments (78.2+/-2.04 microM); however, after 12 h, bioavailability was higher in the 100 microM treatments (56.4+/-24.8 micro) than the 500 microM treatments (13.3+/-1.2 microM). These data suggest that the type of medium determines the degrees and patterns by which metals inhibit biodegradation and emphasize the importance of coupling metal toxicity and bioavailability data.     

PAH depositional history and sources in recent sediment core from Ukwa Ibom Lake, S. E. Nigeria

Analyses of recent sediment core from the Ukwa Ibom Lake show evidence of aquatic production, terrigenous, combustion and petroleum inputs. Total organic carbon/total nitrogen values (>10) for the sediments indicate greater wash-in of land-plant organic matter relative to algal production. The characteristic combustion ratios, fluoranthene/fluoranthene + pyrene (>0.50), anthracene/anthracene + phenanthrene (>0.10), benzo(a)anthracene/benzo(a)anthracene + chrysene (>0.35) as well as 1,7/1,7 + 2,6-dimethylphenanthrene (>0.70) were observed for the top section only. These results coincided with the most recent pave-road extension exercise involving tree logging and burning of bush. The highest total PAH concentration (91.13 ng/g dry weight (dw)) observed for the bottom section coincided with the period of inhabitation of the lake catchments (~5 decades ago) when discharge to the Lake water of domestic sewage and mill waste water were prevalent. The regular decline in total PAH concentrations upcore is a reflection of the ban placed on indiscriminate dumping of wastes following relocation of the inhabitants of the catchments. Besides the local depositional history, the irregular decrease in unresolved complex mixture (UCM) profiles suggests regional contaminant influx from the adjacent upper Cross River estuary, especially during intense rainfall event. The non-uniformity in methylphenanthrene indices (MPI-1 and MPI-2) shows evidence of importation and utilization of petroleum products of different thermal maturity histories into the Nigerian economy.