An analysis of candidates for addition to the Clean Air Act list of hazardous air pollutants

There are 188 air toxics listed as hazardous air pollutants (HAPs) in the Clean Air Act (CAA), based on their potential to adversely impact public health. This paper presents several analyses performed to screen potential candidates for addition to the HAPs list. We analyzed 1086 HAPs and potential HAPs, including chemicals regulated by the state of California or with emissions reported to the Toxics Release Inventory (TRI). HAPs and potential HAPs were ranked by their emissions to air, and by toxicity-weighted (tox-wtd) emissions for cancer and noncancer, using emissions information from the TRI and toxicity information from state and federal agencies. Separate consideration was given for persistent, bioaccumulative toxins (PBTs), reproductive or developmental toxins, and chemicals under evaluation for regulation as toxic air contaminants in California. Forty-four pollutants were identified as candidate HAPs based on three ranking analyses and whether they were a PBT or a reproductive or developmental toxin. Of these, nine qualified in two or three different rankings (ammonia [NH3], copper [Cu], Cu compounds, nitric acid [HNO3], N-methyl-2-pyrrolidone, sulfuric acid [H2SO4], vanadium [V] compounds, zinc [Zn], and Zn compounds). This analysis suggests further evaluation of several pollutants for possible addition to the CAA list of HAPs.     

Flood-risk management strategies for an uncertain future: living with Rhine River floods in The Netherlands?

Social pressure on alluvial plains and deltas is large, both from an economic point of view and from a nature conservation point of view. Gradually, flood risks increase with economic development, because the expected damage increases, and with higher dikes, because the flooding depth increases. Global change, changing social desires, but also changing views, require a revision of flood-risk management strategies for the long term. These should be based on resilience as opposed to the resistence strategy of heightening dikes. Resilience strategies for flood-risk management imply that the river is allowed to temporarily flood large areas, whereas the flood damage is minimized by adapting land use. Such strategies are thus based on risk management and 'living with floods' instead of on hazard control. For The Netherlands, one of the most densely populated deltas in the world, alternative resilience strategies have been elaborated and assessed for their hydraulic functioning and 'sustainability criteria'.     

Degradation of 1,1,2,2-tetrachloroethane and accumulation of vinyl chloride in wetland sediment microcosms and in situ porewater: biogeochemical controls and associations with microbial communities

The biodegradation pathways of 1,1,2,2-tetrachloroethane (TeCA) and 1,1,2-trichloroethane (112TCA) and the associated microbial communities in anaerobic wetland sediments were evaluated using concurrent geochemical and genetic analyses over time in laboratory microcosm experiments. Experimental results were compared to in situ porewater data in the wetland to better understand the factors controlling daughter product distributions in a chlorinated solvent plume discharging to a freshwater tidal wetland at Aberdeen Proving Ground, Maryland. Microcosms constructed with wetland sediment from two sites showed little difference in the initial degradation steps of TeCA, which included simultaneous hydrogenolysis to 112TCA and dichloroelimination to 1,2-dichloroethene (12DCE). The microcosms from the two sites showed a substantial difference, however, in the relative dominance of subsequent dichloroelimination of 112TCA. A greater dominance of 112TCA dichloroelimination in microcosms constructed with sediment that was initially iron-reducing and subsequently simultaneously iron-reducing and methanogenic caused approximately twice as much vinyl chloride (VC) production as microcosms constructed with sediment that was methanogenic only throughout the incubation. The microcosms with higher VC production also showed substantially more rapid VC degradation. Field measurements of redox-sensitive constituents, TeCA, and its anaerobic degradation products along flowpaths in the wetland porewater also showed greater production and degradation of VC with concurrent methanogenesis and iron reduction. Molecular fingerprinting indicated that bacterial species [represented by a peak at a fragment size of 198 base pairs (bp) by MnlI digest] are associated with VC production from 112TCA dichloroelimination, whereas methanogens (190 and 307 bp) from the Methanococcales or Methanobacteriales family are associated with VC production from 12DCE hydrogenolysis. Acetate-utilizing methanogens (acetotrophs) appear to be involved in the biodegradation of VC. The relative abundance of Methanosarcinaceae, the only methanogen group with acetotrophic members, doubled in microcosms in which degradation of VC was observed. In addition, molecular analyses using primers specific for known dehalorespiring bacteria in the Dehalococcoides and Desulfuromonas groups showed the presence of these bacteria in microcosm slurry from the site that showed the highest VC production and degradation. Determination of biogeochemical controls and microbial consortia involved in TeCA degradation is leading to a better understanding of the heterogeneity in biodegradation rates and daughter product distribution in the wetland, improving capabilities for developing remediation and monitoring plans.     

Source characterization of atmospheric heavy metals in industrial/residential areas: a case study in Oman

Total suspended particulate matter (TSP) was collected from two districts: the Sohar industrial estate (SIE) and a residential area in the case study area in Oman. The TSP collected from SIE was taken from 19 different industrial activities, whereas those collected from the residential area were taken from 12 houses. The samples were analyzed for nine heavy metals: chromium (Cr), copper (Cu), manganese (Mn), nickel, lead (Pb), zinc (Zn), cadmium, vanadium, and molybdenum. The results were used to assess the source classes responsible for TSP and heavy metal levels in the atmosphere of the two districts. At each district, principal component analysis was applied to the concentrations of TSP and heavy metals to obtain the number of principal components. At SIE, three groups of elements were determined. The first component contained large factor loadings in Cu and Mn (Cu industrial processes and reinforcement steel production). The second presented most of the variance of Cr, Pb, and Zn (black and galvanized iron pipes production, mechanical industries, and vehicle construction). The third component was composed of Zn and Pb that probably reflected contributions from motor-vehicle tire wear or was associated with municipal incineration. On the other hand, results from the village showed that only one factor was able to explain the main part of the data variance, and the industrial site was polluting air quality in the village with Cu, Cr, Pb, nickel, and Mn.     

Electrochemical decolourisation of structurally different dyes

The electrochemical decolourisation of structurally different dyes (bromophenol blue, indigo, poly R-478, phenol red, methyl orange, fuchsin, methyl green and crystal violet) by means of the application of DC electric current was assessed. It was found that the electrochemical process allowed a colour removal of all dyes studied, although the decolourisation rate largely depended on the chemical structure of the different dyes. Nearly complete decolourisation was achieved for bromophenol blue followed by methyl orange and methyl green, whereas phenol red was hardly decolourised (30% in 60 min). In mixtures of two dyes, the decolourisation rate became similar for both dyes. However, the addition of a redox mediator, (Co(2+/3+)) clearly enhanced the degradation rate of all tested dyes, but the simplest dye molecules were attacked firstly, followed by dyes with more complex chemical structures. The results revealed the suitability of the process to effectively decolourise wastewaters from dyeing process.     

A PCE groundwater plume discharging to a river: influence of the streambed and near-river zone on contaminant distributions

An investigation of a tetrachloroethene (PCE) groundwater plume originating at a dry cleaning facility on a sand aquifer and discharging to a river showed that the near-river zone strongly modified the distribution, concentration, and composition of the plume prior to discharging into the surface water. The plume, streambed concentration, and hydrogeology were extensively characterized using the Waterloo profiler, mini-profiler, conventional and driveable multilevel samplers (MLS), Ground Penetrating Radar (GPR) surveys, streambed temperature mapping (to identify discharge zones), drivepoint piezometers, and soil coring and testing. The plume observed in the shallow streambed deposits was significantly different from what would have been predicted based on the characteristics of the upgradient plume. Spatial and temporal variations in the plume entering the near-river zone contributed to the complex contaminant distribution observed in the streambed where concentrations varied by factors of 100 to 5000 over lateral distances of less than 1 to 3.5 m. Low hydraulic conductivity semi-confining deposits and geological heterogeneities at depth below the streambed controlled the pattern of groundwater discharge through the streambed and influenced where the plume discharged into the river (even causing the plume to spread out over the full width of the streambed at some locations). The most important effect of the near-river zone on the plume was the extensive anaerobic biodegradation that occurred in the top 2.5 m of the streambed, even though essentially no biodegradation of the PCE plume was observed in the upgradient aquifer. Approximately 54% of the area of the plume in the streambed consisted solely of PCE transformation products, primarily cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). High concentrations in the interstitial water of the streambed did not correspond to high groundwater-discharge zones, but instead occurred in low discharge zones and are likely sorbed or retarded remnants of past high-concentration plume discharges. The high-concentration areas (up to 5529 microg/l of total volatile organics) in the streambed are of ecological concern and represent potential adverse exposure locations for benthic and hyporheic zone aquatic life, but the effect of these exposures on the overall health of the river has yet to be determined. Even if the upgradient source of PCE is remediated and additional PCE is prevented from reaching the streambed, the high-concentration deposits in the streambed will likely take decades to hundreds of years to flush completely clean under natural conditions because these areas have low vertical groundwater flow velocities and high retardation factors. Despite high concentrations of contaminants in the streambed, PCE was detected in the surface water only rarely due to rapid dilution in the river and no cDCE or VC was detected. Neither the sampling of surface water nor the sampling of the groundwater from the aquifer immediately adjacent to the river gave an accurate indication of the high concentrations of PCE biodegradation products present in the streambed. Sampling of the interstitial water of the shallow streambed deposits is necessary to accurately characterize the nature of plumes discharging to rivers.     

The uptake of uranium by Eleocharis dulcis (Chinese water chestnut) in the Ranger Uranium Mine constructed wetland filter

Eleocharis dulcis has proliferated in a constructed wetland used to treat uranium mine runoff water, where it rapidly accumulates significant quantities of uranium (U) in its roots and relatively little in its stems. We investigated the mechanism of U uptake and accumulation by E. dulcis using field-sampling techniques and microcosm test work. Results from the microcosm trials and outcomes from statistical tests of field sampled macrophyte, water and sediment indicate that the primary source of U for E. dulcis is the water column. Basipetal translocation of U to the plant's roots was indicated by significant correlations between the U content of stems, taproots and rhizomes and XPS detection of U inside root segments. U sequestering from sediment interstitial water by Fe hydroxides on root surfaces was also evident. No basipetal translocation was evident following the 28-day duration of the microcosm experiments, indicating that it is a longer-term process.     

Sorption and oxic degradation of the explosive CL-20 during transport in subsurface sediments

The abiotic sorption and oxic degradation processes that control the fate of the explosive CL-20, Hexanitrohexaazaisowurtzitane, in the subsurface environment were investigated to determine the potential for vadose and groundwater contamination. Sorption of aqueous CL-20 is relatively small (K(d) = 0.02-3.83 cm3 g(-1) for 7 sediments and 12 minerals), which results in only slight retardation relative to water movement. Thus, CL-20 could move quickly through unsaturated and saturated sediments of comparable composition to groundwater, similar to the subsurface behavior of RDX. CL-20 sorption was mainly to mineral surfaces of the sediments, and the resulting isotherm was nonlinear. CL-20 abiotically degrades in oxic environments at slow rates (i.e., 10s to 100s of hours) with a wide variety of minerals, but at fast rates (i.e., minutes) in the presence of 2:1 phyllosilicate clays (hectorite, montmorillonite, nontronite), micas (biotite, illite), and specific oxides (MnO2 and the ferrous-ferric iron oxide magnetite). High concentrations of surface ferrous iron in a dithionite reduced sediment degraded CL-20 the fastest (half-life < 0.05 h), but 2:1 clays containing no structural or adsorbed ferrous iron (hectorite) could also quickly degrade CL-20 (half-life < 0.2 h). CL-20 degradation rates were slower in natural sediments (half-life 3-800 h) compared to minerals. Sediments with slow degradation rates and small sorption would exhibit the highest potential for deep subsurface migration. Products of CL-20 oxic degradation included three high molecular weight compounds and anions (nitrite and formate). The 2-3.5 moles of nitrite produced suggest CL-20 nitro-groups are degraded, and the amount of formate produced (0.2-1.2 moles) suggests the CL-20 cage structure is broken in some sediments. Identification of further degradation products and CL-20 mineralization rates is needed to fully assess the impact of these CL-20 transformation rates on the risk of CL-20 (and degradation product) subsurface movement.     

Electrochemical monitoring of methylparathion degradation in an acid aqueous medium in presence of Cu(II)

A study was undertaken to determine the effect of Cu(II) in degradation of methylparathion (o,o-dimethyl o,4-nitrophenyl phosphoriotioate) in acid medium. Initial electrochemical characterization of Cu(II) and methylparathion was done in an aqueous medium at a pH range of 2-7. Cu(II) was studied in the presence of different anions and it was observed that its electroactivity depends on pH and is independent of the anion used. Methylparathion had two reduction signals at pH < or = 6 and only one at pH > 6. The pesticide's transformation kinetic was then studied in the presence of Cu(II) in acid buffered aqueous medium at pH values of 2, 4, and 7. Paranitrophenol appeared as the only electroactive product at all three pH values. The reaction was first order and had k values of 5.2 x 10(-3) s(-1) at pH 2, 5.5 x 10(-3) s(-1) at pH 4 and 9.0 x 10(-3) s(-1) at pH 7. It is concluded that the principal degradation pathway of methylparathion in acid medium is a Cu(II) catalyzed hydrolysis reaction.     

Removal of nickel (II) from aqueous solutions using marine macroalgae as the sorbing biomass

In the present study biosorption technique, the passive accumulation of metals by biomass, is used for the removal of nickel from aqueous medium. The brown algae, Sargassum sp., in its natural and acid treated forms are used as a low cost sorbent. The adsorption characteristics of nickel on Sargassum sp. are evaluated as a function of time, pH, adsorbent dosage and initial concentration of nickel. The equilibrium adsorption data are fitted to Freundlich and Langmuir adsorption isotherm models and the model parameters are evaluated. Both the models represent the experimental data satisfactorily. The adsorption follows Lagergren first order kinetic model. The monolayer adsorption capacities of natural and acid treated forms of algae as obtained from Langmuir adsorption model are found to be 181 and 250mg g(-1) respectively.