Bioavailability of hydrophobic organic contaminants and quality of organic carbon

U.S. laws require that contaminant bioaccumulation potential be evaluated before dredged material can be recycled. Simple fugacity models, e.g. organic contaminant aqueous partition coefficient (K _oc)-derived theoretical bioaccumulation potential, are commonly used to estimate the partitioning of hydrophobic organic contaminants between sediment organic matter and organism lipid. K _oc-derived models, with or without the addition of a soot carbon term, did not accurately or consistently predict total polycyclic aromatic hydrocarbons (PAHs) and polychlorobiphenyls partitioning of eight sediments from ongoing dredging operations onto C₁₈-coated filter paper. These models also failed to predict the partitioning of individual PAHs from these eight sediments. These data underscore the trade-offs between the ease of using simple models and the uncertainty of predicted partitioning values.     

Correlation of the partitioning of dissolved organic matter fractions with the desorption of Cd,Cu, Ni,Pb and Zn from 18 Dutch soils

Eighteen Dutch soils were extracted in aqueous solutions at varying pH. Extracts were analyzed for Cd, Cu, Ni, Pb and Zn by ICP-AES. Extract dissolved organic carbon (DOC) was also concentrated onto a macroreticular resin and fractionation into three operationally defined fractions: hydrophilic acids (Hyd), humic acids (HA) and fulvic acids (FA). In this manner, change in absolute solution concentration and relative percentage for each fraction could be calculated as a function of extraction equilibrium pH. The soils were also analyzed for solid phase total organic carbon and total recoverable metals (EPA Method 3051). Partitioning coefficients were calculated for the metals and organic carbon (OC) based on solid phase concentrations (less the metal or OC removed by the extraction) divided by solution concentrations. Cu and Pb concentrations in solution as a function of extract equilibrium pH are greatest at low and high pH resulting in parabolic desorption/dissolution curves. While processes such as proton competition and proton promoted dissolution can account for high solution metal concentrations at low pH, these processes cannot account for higher Cu and Pb concentrations at high pH. DOC increases with increasing pH, concurrently with the increase in Cu and Pb solution concentrations. While the absolute concentrations of FA and HA generally increase with increasing pH, the relative proportional increase is greatest for HA . Variation in HA concentrations spans three orders of magnitude while FA concentrations vary an order of magnitude over the pH range examined. Correlation analysis strongly suggests that HA plays a major role in increasing the concentration of solution Cu and Pb with increasing pH in the 18 soils studied. The percentage of the OC that was due to FA was nearly constant over a wide pH range although the FA concentration increased with increasing pH and its concentration was greater than that of the HA fraction at lower pH values (pH = 3-5). Thus, in more acidic environments, FA may play a larger role than HA in governing organo-metallic interactions. For Cd, Ni, and Zn, the desorption/dissolution pattern shows high metal solution concentrations at low pH with slight increases in solution concentrations at extremely high pH values (pH>10). The results presented here suggest that the effects of dissolved organic carbon on the mobilization of Cd, Ni, and Zn may only occur in systems governed by very high pH. At high pH, it is difficult to distinguish in this study whether the slightly increased solution-phase concentrations of these cations is due to DOC or hydrolysis reactions. These high pH environments would rarely occur in natural settings.     

Vertical distribution of radionuclides in soil of a grassland site in Chernobyl exclusion zone

Five soil profiles from a site about 8 km SE of the Chernobyl NPP were investigated for the vertical distribution of radionuclides. The average (137)Cs-inventory at the site is about 2.6 MBq/m(2) (reference date 1 May 1986). Apart from (137)Cs, the following radionuclides have been identified (their activity ratios to (137)Cs in brackets): (134)Cs (0.537), (125)Sb (0.068), (60)Co (0.0022), (154)Eu (0.016), (155)Eu (0.020), (94g)Nb (9.5E-5), (239/240)Pu (0.0088), (238)Pu (0.040), (90)Sr (0.30) and (241)Am (0.011). Apparent vertical migration velocities are between 0.14 and 0.26 cm/a, apparent dispersion coefficients range from 0.02 to 0.13 cm(2)/a. The rankings of the velocities v for different radionuclides are (Sr, Cs, Sb, Co, Pu)< Am < Eu and Sr < (Cs, Nb), for D, the following rankings have been found: (Nb, Sr, Cs) < Am < Eu, Cs相似文献   

The chemical and mineralogical behaviour of Pb in shooting range soils from central Sweden

Recently investigations have shown that the annual flux of lead from shotgun pellets to shooting range soils is significant in some countries. This paper presents the data of chemical and mineralogical analyses of soils and Pb-pellet crusts from five shooting ranges in Sweden and, based on these results, evaluates the retention of lead in these shooting range soils. In the soils, Pb-pellets and bullets are readily decomposed and transformed to crust materials composed of Pb-bearing minerals. The transformation products in the crust materials, identified by X-ray diffraction, are predominantly hydrocerussite [Pb(3)(CO(3))(2) (OH)(2)], associated with cerussite (PbCO(3)) and anglesite (PbSO(4)). In a period of 20-25 years, an average of 4.8% metallic lead in the pellets has been transformed to lead carbonate and lead sulphate, where the former is the more stable mineral in the surface environment. However, in soils relatively rich in humus an average of 15.6% metallic lead in the pellets was transformed to secondary lead compounds in the same period. The results of the chemical analyses indicate that Pb is rather immobile in the soil profile. The surficial horizon contains higher concentrations of lead (52-3400 mg kg(-1)), while lower concentrations of lead were found in the E and B horizons where the total Pb concentrations (8-37 mg kg(-1)) are within about one standard deviation of the mean reference sample concentration. An inverse relationship is revealed between the aluminium hydroxide content of the soil fraction and EDTA-extractable Pb, which suggests that these compounds have affected the retention of lead.     

A performance-based framework for demonstrating appropriate use of an alternate method for wastewater compliance monitoring.

The choice of wastewater compliance methods used in the United States has been largely prescribed; however, in some cases, this has led to data of unknown or poor quality. This problem is further compounded by the relatively slow regulatory approval process to incorporate discharge-specific method modifications or flexibility to using alternate, potentially better technologies. In this study, a framework is presented, using a performance-based-system approach, which a discharger could use to verify proper use of an alternate or modified method. An example, using two chemical oxygen demand methods (a currently approved method and an alternate method that does not generate hazardous waste) demonstrates that the protocol is simple to use, yet scientifically defensible and effective and that this approach should be readily understandable to both regulators and the regulated community. Our results also suggest that the reference method approach, without associated measurement quality objectives, may yield a false sense of competency with an alternate method.     

Studies of the oxidative photoinduced degradation of silicones in the aquatic environment

During irradiation of aqueous solutions of a mixture of oligomeric dimethylsiloxanes with artificial sunlight in the presence of nitrate ions, a reduction in the concentration of the siloxanes was demonstrated. This was verified by atomic absorption spectroscopy and proton nuclear magnetic resonance spectroscopy.In two separate tests, average halflives of 9 and 4 days, respectively, were determined after extraction of the aqueous solutions and analysis by atomic absorption spectroscopy.Silicate was demonstrated to be the final photodegradation product of these water soluble siloxanes. Photometric determination of silicate after 35 days showed nearly complete transformation, based on the original quantity of siloxanes.When an aqueous emulsion of high molecular-weight poly(dimethylsiloxane) was irradiated in the presence of nitrate ions under similar experimental conditions, a level of silicate corresponding to 1.7% of the original quantity of poly(dimethylsiloxane) was found after 5 weeks.     

Resprouting as a persistence strategy of tropical forest trees: relations with carbohydrate storage and shade tolerance

Resprouting is an important persistence strategy for woody species and represents a dominant pathway of regeneration in many plant communities, with potentially large consequences for vegetation dynamics, community composition, and species coexistence. Most of our knowledge of resprouting strategies comes from fire-prone systems, but this cannot be readily applied to other systems where disturbances are less intense. In this study we evaluated sapling responses to stem snapping for 49 moist-forest species and 36 dry-forest species from two Bolivian tropical forests. To this end we compared in a field experiment the survival and height growth of clipped and control saplings for a two-year period, and related this to the shade tolerance, carbohydrate reserves, and the morphological traits (wood density, leaf size) of the species. Nearly all saplings resprouted readily after stem damage, although dry-forest species realized, on average, a better survival and growth after stem damage compared to moist-forest species. Shade-tolerant species were better at resprouting than light-demanding species in moist forest. This resprouting ability is an important prerequisite for successful regeneration in the shaded understory, where saplings frequently suffer damage from falling debris. Survival after stem damage was, surprisingly, only modestly related to stem reserves, and much more strongly related to wood density, possibly because a high wood density enables plants to resist fungi and pathogens and to reduce stem decay. Correlations between sampling performance and functional traits were similar for the two forest types, and for phylogenetically independent contrasts and for cross-species analyses. The consistency of these results suggests that tropical forest species face similar trade-offs in different sites and converge on similar sets of solutions. A high resprouting ability, as well as investments in stem defense and storage reserves, form part of a suite of co-evolved traits that underlies the growth-survival trade-off, and contributes to light gradient partitioning and species coexistence. These links with shade tolerance are important in the moist evergreen forest, which casts a deep, more persistent shade, but tend to diminish in dry deciduous forest where light is a less limiting resource.     

Allocation in reproduction is not tailored to the probable number of matings in common toad (<Emphasis Type="Italic">Bufo bufo</Emphasis>) males

The theory of life history evolution assumes trade-offs between competing fitness traits such as reproduction, somatic growth, and maintenance. One prediction of this theory is that if large individuals have a higher reproductive success, small/young individuals should invest less in reproduction and allocate more resources in growth than large/old individuals. We tested this prediction using the common toad (Bufo bufo), a species where mating success of males is positively related to their body size. We measured testes mass, soma mass, and sperm stock size in males of varying sizes that were either (1) re-hibernated at the start of the breeding season, (2) kept without females throughout the breeding season, or (3) repeatedly provided with gravid females. In the latter group, we also estimated fertilization success and readiness to re-mate. Contrary to our predictions, the relationship between testes mass and soma mass was isometric, sperm stock size relative to testes mass was unrelated to male size, fertilization success was not higher in matings with larger males, and smaller males were not less likely to engage in repeated matings than larger males. These results consistently suggest that smaller males did not invest less in reproduction to be able to allocate more in growth than larger males. Causes for this unexpected result may include relatively low year-to-year survival, unpredictable between-year variation in the strength of sexual selection and low return rates of lowered reproductive investment.