Perchlorate: Problems,Detection, and Solutions

The perchlorate anion (ClO 4 m ) is produced when the solid salts of ammonium, potassium, and sodium perchlorate, and perchloric acid dissolve in water. Ammonium perchlorate, used in solid rocket engine fuels, has a limited shelf life and must periodically be replaced. Before 1997, perchlorate could not be readily detected in groundwater at concentrations below 100 µg/L, until the California Department of Health Services developed an acceptable analytical method that lowered the detection limit to 4 µg/L. Subsequently, groundwater containing perchlorate were soon encountered in several western states, and contamination became apparent in Colorado River water. Most perchlorate salts have high water solubilities; concentrated solutions have densities greater than water. Once dissolved, perchlorate is extremely mobile, requiring decades to degrade. Health effects from ingesting low dosage perchlorate-contaminated water are not well known: it interferes with the body's iodine intake, causing an inhibition of human thyroid production. Contaminated surface and groundwater treatment may require bio- and/or phytoremediation technologies. Perchlorate in groundwater is relatively unretarded; it probably travels by advection. Therefore, it may be used as a tracer for hydrocarbon and metal contaminants that are significantly more retarded. Possible forensic techniques include chlorine isotopes for defining multiple or commingled perchlorate plumes.     

Impact of unconfined sulphur-mine waste on a semi-arid environment (Almería, SE Spain)

Thirty-five soil samples were taken from unconfined mine waste, stream sediments, and surfaces unoccupied by mining and presumably unaffected by it, in a sulphur-mining zone surrounded by carbonate material and characterized by a semi-arid climate with short torrential storms. These samples were analysed and the results compared to estimate the spread of pollution in the landscape and to assess potential environmental risk. The mean concentrations of S, Zn, Cd, Pb, and As in mine waste were between 3.5-fold (As) and 50-fold (S) greater than unaffected soils. Oxidation of S led to a sharp drop in pH, strong weathering of minerals, and solubilisation of the constituent elements, forming a toxic acidic mine drainage with highly concentrated pollutants that were discharged into the drainage channels. Successive acid mine drainage into the soil on the valley floor spreads acidification and pollution downstream. The high carbonate content in surrounding soils played an important role in the increase of the pH and precipitation of S, Pb, and Al of the affected soils. Meanwhile, high mobility of Zn, Cd and As under basic conditions and a low Fe concentration explain the broad spread of these elements, as high concentrations were detected in soil more than 2000 m from the source. Only the soil solutions from near the waste dump (first 500 m) were highly phytotoxic, and moderately phytotoxic from 500 to 1500 m away. The concentration of pollutants in the leachates was clearly higher than in soil solutions, even in the soils located over 2000 m from the source, implying that the size of the polluted area will increase with time.     

Metals in particle-size fractions of the soils of five European cities

Soils from Aveiro, Glasgow, Ljubljana, Sevilla and Torino have been investigated in view of their potential for translocation of potentially toxic elements (PTE) to the atmosphere. Soils were partitioned into five size fractions and Cr, Cu, Ni, Pb and Zn were measured in the fractions and the whole soil. All PTE concentrated in the <10 microm fraction. Cr and Ni concentrated also in the coarse fraction, indicating a lithogenic contribution. An accumulation factor (AF) was calculated for the <2 and <10 microm fraction. The AF values indicate that the accumulation in the finer fractions is higher where the overall contamination is lower. AF for Cr and Ni are particularly low in Glasgow and Torino. An inverse relationship was found between the AF of some metals and the percentage of <10 microm particles that could be of use in risk assessment or remediation practices.     

表面活性剂淋洗与投菌法联合修复2,4,6-三氯苯酚污染土壤

为了解决高浓度氯酚土壤污染问题,提出了一种表面活性剂淋洗与投菌法相结合的土壤修复方法。该方法采用表面活性剂淋洗污染土壤,使高浓度氯酚得到大部分去除后再加入微生物降解菌,从而实现低浓度氯酚的持续降解。通过2,4,6-三氯苯酚(2,4,6-TCP)的增溶实验、吸附实验以及表面活性剂的酶抑制实验,对蔗糖酯(SE)、鼠李糖脂(RL)、茶皂素(TS)、脂肪醇聚氧乙烯醚(AEO-9)4种表面活性剂进行了筛选。结果表明,SE增溶、解吸的综合效果较好,且具备良好的生物相容性,适用于淋洗有机污染土壤。淋洗-投菌联合实验表明,以0.5wt%蔗糖酯水溶液作为淋洗剂淋洗土壤并投菌降解,25 d内土壤中的2,4,6-三氯苯酚从190.4降至3.1 mg/kg,去除率达到98.4%。     

Contents of heavy metals in marine seaweeds from the Egyptian coast of the Red Sea

Seaweeds belonging to 14 different genera of Chlorophyta, Phaeophyta, and Rhodophyta were analysed to determine the levels of heavy metals in two areas of the Egyptian Red Sea coast. Among the trace metals analysed, Mn and Zn showed the highest mass concentrations in the surface sea waters of the two studied areas. However, algae obtained from the Suez area had higher concentrations of the investigated heavy metals than those collect in the Mars Alam area. Nevertheless, a high variability of the metal levels occurs among the studied algae and also between the investigated areas. Moreover, Zn was the most abundant metal in the seaweeds of the Suez area, while Pb was predominant in the Mars Alam area in red and brown algae. Liagora spp. had the highest average concentration factor of Zn in Suez (29 161-fold), while the average concentration factor in Enteromorpha spp. at Mars Alam was 20 091-fold. The highest Metal Pollution Index (MPI) value was recorded in Liagora spp. (22.0) at Suez. This represents a 4.6-fold higher value than that recorded in Liagora spp. at Mars Alam. Among green, brown, and red algae in Suez, the highest values of MPI were recorded in Cladophora spp. and Halimeda spp. (18.2 and 18.3), Padina spp. (16.2), and Liagora spp. (22.1), respectively; while at Mars Alam, the highest values of MPI were recorded in Cladophora spp. (6.6), Padina spp. (3.4) and Liagora spp. (4.8), respectively.     

PESTICIDE OCCURRENCE IN GROUNDWATER IN TULARE COUNTY, CALIFORNIA

Geographic Information Systems (GIS) and statistical methodswere used to identify the major factors affecting pesticideleaching in groundwater from agricultural fields in TulareCounty, California. Residues of bromacil, diuron, and simazineincreased in groundwater during the 1980s. Bromacil, diuron,and simazine contamination were positively correlated to cropdiversity and water demand. Diuron and simazine were positively correlated to groundwater depth and negatively correlatedto soil water-holding capacity. DBCP concentration in groundwater was related to the crop coverage. The Goss model wasused to examine soil-pesticide interactions and a PesticideContamination Index (PCI) was developed. Areas having highleaching potentials were mainly associated with citrus andorchards and coarse-textured sandy soils along the SierraNevada foothills, while areas having low leaching potentialswere associated with field crops and clay soils of the southwest region. The PCI was largest for DBCP during the 1980s,suggesting that it was the most significant contaminant before1977 when it was widely used; however, wells were not testedfor this pesticide during that period. Twelve years after DBCPwas banned, it was still the most significant health riskcontaminant. Spatial maps showing the distribution of leachingpotentials and soil interactions for these pesticides canprovide useful information to regulatory and planning agenciesfor land use planning and pesticide management.     

A cation exchange model to describe Cs+ sorption at high ionic strength in subsurface sediments at Hanford site, USA

A theoretical and experimental study of cation exchange in high ionic strength electrolytes was performed using pristine subsurface sediments from the U.S. Department of Energy Hanford site. These sediments are representative of the site contaminated sediments impacted by release of high level waste (HLW) solutions containing 137Cs+ in NaNO3 brine. The binary exchange behavior of Cs+-Na+, Cs+-K+, and Na+-K+ was measured over a range in electrolyte concentration. Vanselow selectivity coefficients (Kv) that were calculated from the experimental data using Pitzer model ion activity corrections for aqueous species showed monotonic increases with increasing electrolyte concentrations. The influence of electrolyte concentration was greater on the exchange of Na+-Cs+ than K+-Cs+, an observation consistent with the differences in ion hydration energy of the exchanging cations. A previously developed two-site ion exchange model [Geochimica et Cosmochimica Acta 66 (2002) 193] was modified to include solvent (water) activity changes in the exchanger phase through application of the Gibbs-Duhem equation. This water activity-corrected model well described the ionic strength effect on binary Cs+ exchange, and was extended to the ternary exchange system of Cs+-Na+-K+ on the pristine sediment. The model was also used to predict 137Cs+ distribution between sediment and aqueous phase (Kd) beneath a leaked HLW tank in Hanfordd's S-SX tank using the analytical aqueous data from the field and the binary ion exchange coefficients for the pristine sediment. The Kd predictions closely followed the trend in the field data and were improved by consideration of water activity effects that were considerable in certain regions of the vadose zone plume.     

京沪高速公路"3.29"液氯泄漏污染事故简析

剖析了京沪高速公路江苏段“3．29”液氯泄漏污染事故产生的原因和对生态环境的危害,提出了防范类似事故再次发生的初步设想。     

Effect of cropping systems on the mobility and uptake of Cd and Zn

A field experiment was carried out to determine the effect of different land use systems such as continuous grass and agricultural crops rotation on the bioavailability of heavy metals in soils contaminated by former excessive sewage sludge application. The results show that Cd and Zn concentrations increased to 2 and 3.5 folds within 3 cuts of grass, respectively. Even 10 years after the end of excessive sewage sludge application the concentration of Cd in winter and summer wheat is 3.4 and 2.5 folds higher than the control, respectively. Zn concentration increased by two folds for both crops. In conclusion, the uptake depends on plant species and the degree of soil contamination. The availability of heavy metals was not changed with time.     

Metal pollution in sediments of Jamaica Bay,New York,USA—An urban estuary

Calculations of the annual input of heavy metals to Jamaica Bay, New York, USA, reveal that sewage effluent carries the largest quantities of Ni, Zn, Cu, and Cd to the bay. Storm sewers and atmospheric fallout are the main sources of Pb. Atmospheric fallout of Zn, Cu, and Cd, although smaller than the combined input from sewers, contributes a significant fraction of these metals. The metal input from landfill leachate is far smaller than that from other sources. Analysis of available data shows that metal concentrations in the sediment of the bay correlate with each other and with percent total organic carbon (%TOC). This is consistent with the observation that the input of metals is predominantly associated with sewage. It is demonstrated that metal-TOC ratios, rather than metal concentrations, must be used in efforts to detect local intensive sources of metals in solution; metal-TOC ratios in intertidal sediment adjacent to these landfills are elevated by the adsorption of leachate metals, while metal concentrations are not. Subtidal sediment within a few hundred meters from two landfills shows no evidence of the addition of metals from that source, which is consistent with the small input of metals estimated for these landfills. The evidence cited in this study sharply contradicts the implication made in a widely publicized report issued by an environmental advocacy group that a significant link exists between metals found in subtidal sediment of Jamaica Bay and landfill leachate.