Degradation of polycyclic aromatic hydrocarbons by combined chemical pre-oxidation and bioremediation in creosote contaminated soil

The ability of pre-oxidation to overcome polycyclic aromatic hydrocarbons (PAH) recalcitrance to biodegradation was investigated in creosote contaminated soil. Sand and peat artificially spiked with creosote (quality WEI C) were used as model systems. Ozonation and Fenton-like treatment were proved to be feasible technologies for PAH degradation in soil. The efficiency of ozonation was strongly dependent on the water content of treated soil samples. The removal of PAH by Fenton-like treatment depended on the applied H2O2/soil weight ratio and ferrous ions addition. It was determined that the application of chemical oxidation in sand resulted in a higher PAH removal and required lower oxidant (ozone, hydrogen peroxide) doses. The enhancement of PAH biodegradability by different pre-treatment technologies also depended on the soil matrix. It was ascertained that combined chemical and biological treatment was more efficient in PAH elimination in creosote contaminated soil than either one alone. Thus, the combination of Fenton-like and the subsequent biological treatment resulted in the highest removal of PAH in creosote contaminated sand, and biodegradation with pre-ozonation was found to be the most effective technology for PAH elimination in peat.     

Visitor-induced changes in the chemical composition of soils in backcountry areas of Mt Robson Provincial Park, British Columbia, Canada

Balancing recreation and conservation is an important issue in Canada's parks and protected areas. Increased levels of visitation to parks, especially to backcountry areas, create undue pressure on natural resources, resulting in a variety of ecological impacts. This paper illustrates the issue of visitor-induced changes on the chemical composition of soils in Mt Robson Provincial Park, British Columbia. Soil samples were collected from dish wash stations and fire pits (disturbed sites) at seven campgrounds located along two popular backcountry trails, and were compared to samples obtained from adjacent undisturbed control sites. Analysis of soil samples suggest that the lower amounts of aluminum, potassium, magnesium and sodium in many of the 'disturbed' samples can be related to intense leaching in dish wash stations, and can be attributed to frequent disposal of waste water from washing and cooking activities. Soils in wash stations generally had higher phosphorus, copper and zinc contents as compared to controls. Soils in fire pits were elevated in copper, relative to controls. Results of this study support park regulations that waste water disposal and camp fires be restricted to designated areas. Informing the public of scientific studies helps them understand the consequences of their activities; this may help persuade them to observe park rules and regulations.     

Decision making under uncertainty in case of soil remediation

Decisions on soil remediation are one of the most difficult management issues of municipal and state agencies. The assessment of contamination is uncertain, the costs of remediation are high, and the impacts on the environment are multiple. This paper presents a general, transparent, and consistent method for decision making among the remediation alternatives. Soil washing, phytoremediation, and no remediation are exemplarily considered. Multi-criteria utility functions including (a) the cost of remediation (b) the impact on human health and agricultural productivity, and (c) the economic gain after remediation are constructed using probability density functions representing contamination for all site coordinates. Herewith, the probability of different types of (i) correct decisions such as a hit or a true rejection and (ii) erroneous decisions such as a false alarm or miss are examined. The decision theoretic model is applied to a case study on heavy metal contaminated soil. This case study reveals the non-linear structure of multi-criteria-decision making. The case study shows that the geostatistical uncertainties of the log-normal distributed soil contamination must be taken into account: When uncertainties are not considered and the utilities are assessed according to the estimated value for a spatial unit, only few (N=26) spatial units result where the utility score of the alternative soil washing are higher than the utility score to the no remediation alternative. However, when taking into account geostatistical uncertainties of the log-normal soil distribution this number is about ten times greater (N=237). Furthermore, the use of 'maximizing expected utility' as decision rule is critical in that it may lead to a high probability of misses.     

An efficient technology to treat heavy metal--lead--contaminated soil by microwave radiation

Microwave (MW) technology can be used to vitrify contaminated soil wastes and immobilize heavy metal ions in soils. More than 93% of the Pb(II)-contaminated soil was vitrified to a glass/ceramic formation after 30 min of MW radiation. In a 6-year study, the Pb(II) concentration of the vitrified soil in the leaching test was less than 1.0 mg/l, which is substantially below the USEPA regulatory limit of 5.0 mg/l.     

Fish mercury increase in Lago Manso, a new hydroelectric reservoir in tropical Brazil

It has been frequently demonstrated that mercury (Hg) concentrations in fish rise in newly constructed hydroelectric reservoirs in the Northern Hemisphere. In the present work, we studied whether similar effects take place also in a tropical upland reservoir during impoundment and discuss possible causes and implications. Total Hg concentrations in fish and several soil and water parameters were determined before and after flooding at Rio Manso hydroelectric power plant in western Brazil. The Hg concentrations in soil and sediment were within the background levels in the region (22-35 ng g(-1) dry weight). There was a strong positive correlation between Hg and carbon and sulphur in sediment. Predatory fish had total Hg concentrations ranging between 70 and 210 ng g(-1) f.w. 7 years before flooding and between 72 and 755 ng g(-1) f.w. during flooding, but increased to between 216 and 938 ng g(-1) f.w. in the piscivorous and carnivorous species Pseudoplatystoma fasciatum, cachara, and Salminus brasiliensis, dourado, 3 years after flooding. At the same time, concentrations of organic carbon in the water increased and oxygen concentrations decreased, indicating increased decomposition and anoxia as contributing to the increased Hg concentrations in fish. The present fish Hg concentrations in commonly consumed piscivorous species are a threat to the health of the population dependent on fishing in the dam and downstream river for sustenance. Mercury exposure can be reduced by following fish consumption recommendations until fish Hg concentrations decrease to a safe level.     

Determination of Frequency for Remeasuring Ground and Vegetation Cover Factor Needed for Soil Erosion Modeling

Determining a remeasurement frequency of variables over time is required in monitoring environmental systems. This article demonstrates methods based on regression modeling and spatio-temporal variability to determine the time interval to remeasure the ground and vegetation cover factor on permanent plots for monitoring a soil erosion system. The spatio-temporal variability methods include use of historical data to predict semivariograms, modeling average temporal variability, and temporal interpolation by two-step kriging. The results show that for the cover factor, the relative errors of the prediction increase with an increased length of time interval between remeasurements when using the regression and semivariogram models. Given precision or accuracy requirements, appropriate time intervals can be determined. However, the remeasurement frequency also varies depending on the prediction interval time. As an alternative method, the range parameter of a semivariogram model can be used to quantify average temporal variability that approximates the maximum time interval between remeasurements. This method is simpler than regression and semivariogram modeling, but it requires a long-term dataset based on permanent plots. In addition, the temporal interpolation by two-step kriging is also used to determine the time interval. This method is applicable when remeasurements in time are not sufficient. If spatial and temporal remeasurements are sufficient, it can be expanded and applied to design spatial and temporal sampling simultaneously.     

Effect of Cadmium on Microbial Activity and a Ryegrass Crop in Two Semiarid Soils

Soil pollution with Cd is an environmental problem common in the world, and it is necessary to establish what Cd concentrations in soil could be dangerous to its fertility from toxicity effects and the risk of transference of this element to plants and other organisms of the food chain. In this study, we assessed Cd toxicity on soil microorganisms and plants in two semiarid soils (uncultivated and cultivated). Soil ATP content, dehydrogenase activity, and plant growth were measured in the two soils spiked with concentrations ranging from 3 to 8000 mg Cd/kg soil and incubated for 3 h, 20 days, and 60 days. The Cd concentrations that produced 5%; 10%;, and 50%; inhibition of each of the two soil microbiological parameter studied (ecological dose, ED, values) were calculated using two different mathematical models. Also, the effect of Cd concentration on plant growth of ryegrass (Lolium perenne, L.) was studied in the two soils. The Cd ED values calculated for soil dehydrogenase activity and ATP content were higher in the agricultural soils than in the bare soil. For ATP inhibition, higher ED values were calculated than for dehydrogenase activity inhibition. The average yields of ryegrass were reduced from 5.03 to 3.56 g in abandoned soil and from 4.21 to 1.15 g in agricultural soil with increasing concentrations of Cd in the soil. Plant growth was totally inhibited in abandoned and agricultural soils at Cd concentrations above 2000 and 5000 mg/kg soil, respectively. There was a positive correlation between the concentration of Cd in the plants and the total or DTPA-extractable concentrations of Cd in the soil.     

流动注射-氢化物发生-原子荧光光谱法测定土壤中铅

采用流动注射-氢化物发生-原子荧光光谱法测定土壤中的铅,工作曲线线性关系良好,检出限为0.25 mg/kg,相对标准偏差＜3.5%,加标回收率为93.0%～105%.该方法简便快速,测定结果准确可靠.     

不同氮源和曝气方式对淡水藻类生长的影响

利用水族箱微宇宙研究了2种氮源水体中不同曝气条件对藻类生长的影响.试验使用铵态氮(NH₄⁺-N)和硝态氮(NO₃^--N)作为氮源,每种氮源水体分别设置不曝气、连续曝气、昼间曝气和夜间曝气4个处理.结果显示:试验初期以NH₄⁺-N为主要氮源的水体中藻类生长明显好于以NO₃^--N为主要氮源的水体.试验后期则以NO₃^--N为主要氮源的藻类生长情况更好.连续曝气对于2种氮源水体中藻类生长有着不同的影响;昼间曝气对2种氮源的藻类生长影响不大;而夜间曝气对藻类生长有明显的抑制作用.NH₄⁺-N含量较高的水体中蓝藻容易成为优势种,而NO₃^--N含量高的水体中则以绿藻为主.不同曝气条件下藻类优势种没有明显差别.     

磷对云龙湖富营养化优势藻及混合藻生长的影响

氮磷等营养盐的增加和藻类的过度增殖是富营养化的主要标志。大多数湖泊水体富营养化受磷元素的制约。研究表明富营养化水体的不同藻类对磷含量的依赖性各不相同。通过研究在相同氮浓度,相同温度条件下,不同磷浓度对纯种小球藻和硅藻以及天然混合藻生长速度的影响,发现在氮浓度充足的情况下,磷含量高促进小球藻生长;对硅藻却没有明显的相关性;天然水体混合藻生长速度与磷浓度呈正相关。