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1.
The quality of the water from 62 home wells in a section (with no sewerage system) of the agricultural-industrial area of La Plata, was analyzed. The measurement of the studied parameters concentrations were compared with those obtained in seventeen water wells located in another area of town, with commercial characteristics. The pH, total dissolved salts (TDS), nitrates, chlorides, total hardness (TH) and coliform bacteria, these being differentiated between colifaecals and IAC group bacteria, were studied. The average concentration of TDS was 619 and 497 mg L-1 respectively. 34% of the samples exceeded the limit of 45 mg L-1 established by the World Health Organization (WHO). The nitrate levels varied widely from 6 to 216 mg L-1, with an average value of 56 mg L-1 in the agricultural area, and between 5 and 61 mg L-1 in the commercial area, with an average of 19 mg L-1. The average concentrations of chlorides and TH were 89 mg L-1 and 177 mg L-1, respectively in the agricultural area; while in the other area, the average levels were 38 mg L-1 chloride and 107 mg L-1 TH. Significant differences were observed between the chemical parameters evaluated in the two areas analyzed. E. Coli bacterium was detected in 49% of the well water samples analyzed. IAC group bacteria were confirmed in 28% of the samples. The average depth of the water wells within 10 m from the cesspits was 28.2 m, and those situated farther than 10 m. had an average of 39.9 m depth. Results indicated a remarkable quality degradation of the well waters as regards their contents of E. Coli bacteria and nitrate. This could be due to the deficient construction of the absorption wells, to their closeness with cesspits and the inexistence of septic chambers within every dwelling.  相似文献   

2.
Agricultural, urban, forest and groundwater protection areas as well as nitrate and chloride concentrations are documented in maps. Areal distribution shows regionally elevated nitrate and chloride concentrations in connection with urban areas and agricultural use. Transport of nitrate and chloride tends to be conservative in the groundwater of the investigated area. Therefore, the elevated concentrations of these anions are suitable as indicators of anthropogenic impact on the groundwater. The average concentration of nitrate and chloride from all surveyed wells amounts to 26 and 17 mg L?1, respectively. It is shown that wells recharged through forests have lower nitrate and chloride concentrations (average: 21 and 13 mg L?1, respectively). Wells affected by waste deposits have an average nitrate concentration of 35 mg L?1 and chloride concentration of 24 mg L?1. Urban use results in an average value of 28 mg L?1 nitrate and 24 mg L?1 chloride. As nitrate and chloride concentrations are stable with respect to the depth of the groundwater table, degradation processes or other protective effects of the unsaturated zone can be omitted.  相似文献   

3.
The quality of 109 water samples, comprised of 70 drinking waterand 39 irrigation water samples, in Al-Gassim Region of SaudiArabia was investigated with respect to total dissolved salts(TDS), electric conductivity (EC), pH, total hardness and themajor cations (Ca2+, Mg2+, Na+ and K+) andanions (Cl-, SO4 2-, NO3 -,F- andHCO3 -) beside coliform bacteria as an indicator offaecal contamination.The concentrations of TDS varied widely, from 109 to 6995 mgL-1, with a mean of 1427 mg L-1. Of the 109 watersamples examined, 81 (74.3%) comply with the maximumpermissible drinking water limits set by the local and international standards and guidelines and 28 (25.7%) were abovethe limits of these standards. The concentrations of the cationsand anions (with the exception of NO3 - and F-)follow, more or less, a trend similar to TDS. NO3 - concentrations (range 0–30 mg L-1) comply with the limitof 50 mg L-1 NO3 - as the highest tolerableNO3 - content. The concentrations of F- indrinking water (range 0.2–1.5 mg L-1) are alarming since88% of samples were below the lower permissible limit of 0.6 mgL-1 set by SASO (1984), the guideline of the WHO is 1.5 mgL-1 while the EEC maximum concentration lies within the range 0.7–1.5 mg L-1. Microbiological analyses showednegative coliform tests, which confirms that they are devoid ofany faecal contamination.  相似文献   

4.
Outwintering beef cattle on woodchip corrals offers stock management, economic and welfare benefits when compared with overwintering in open fields or indoors. A trial was set up on a loamy sand over sand soil to evaluate the pollution risks from corrals and the effect of design features (size and depth of woodchips, stocking density, and feeding on or off the corral). Plastic‐lined drainage trenches at 9–10 m spacing under the woodchips allowed sampling of the leachate. Sampling of the soil to 3.6 m below the corral allowed evaluation of pollutant mitigation during vadose zone transport. Mean corral leachate pollutant concentrations were 443–1056 mg NH4‐N L?1, 372–1078 mg dissolved organic carbon (DOC) L?1, 3–13 mg NO3‐N L?1, 8 × 104–1.0 × 106Escherichia coli 100 mL?1 and 2.8 × 102–1.4 × 103 faecal enterococci 100 mL?1. Little influence of design features could be observed. DOC, NH4 and (in most cases) E. coli and faecal enterococci concentrations decreased 102–103 fold when compared with corral leachate during transport to 3.6 m but there were some cores where faecal enterococci concentrations remained high throughout the profile. Travel times of pollutants (39–113 days) were estimated assuming vertical percolation, piston displacement at field moisture content and no adsorption. This allowed decay/die‐off kinetics in the soil to be estimated (0.009–0.044 day?1 for DOC, 0.014–0.045 day?1 for E. coli and 0–0.022 day?1 for faecal enterococci). The mean [NO3‐N] in pore water from the soil cores (n = 3 per corral) ranged from 114 ± 52 to 404 ± 54 mg NO3‐N L?1, when compared with 59 ± 15 mg NO3‐N L?1 from a field overwintering area and 47 ± 40 mg NO3‐N L?1 under a permanent feeding area. However, modelling suggested that denitrification losses in the soil profile increased with stocking density so nitrate leaching losses per animal may be smaller under corrals than for other overwintering methods. Nitrous oxide, carbon dioxide and methane fluxes (measured on one occasion from one corral) were 5–110 g N ha?1 day?1, 3–23 kg C ha?1 day?1, and 5–340 g C ha?1 day?1 respectively. Ammonia content of air extracted from above the woodchips was 0.7–3.5 mg NH4‐N m?3.  相似文献   

5.
This paper presents the results of monitoring the shallow groundwater quality around two municipal landfill sites in the Eastern Province of Saudi Arabia. Boreholes were installed at Dhahran and Juaymah sites upstream and downstream of the landfill. Twenty water samples were collected from each borehole and analyzed for various parameters mainly for BOD, COD, TOC, NH3-N, TKN, sulphate, chloride, hardness and metals. The result of the analysis of water samples from Dhahran boreholes shows an increase in the concentration of pollutants in downstream groundwater over that observed in upstream boreholes. The average concentration of BOD5, COD and TOC in the samples obtained from the downstream borehole was found to be 6.5, 23.5, and 34.3 mg L?1, respectively. On the other hand, the mean concentration of the same parameters in upstream monitoring wells was found to be less than 2.4, 11.5, and 10.0 mg L?1, respectively. The ammonia-N and organic-N in the downstream wells were 0.37 and 0.29 mg L?1, respectively, whereas, in upstream wells they were 0.11 and 0.15 mg L?1, respectively. At Juaymah, the average concentration of BOD and TOC in groundwater samples obtained from upstream boreholes were less than 3.0 and 7.2 mg L?1, respectively, while the concentration of the same parameters in downstream well samples were above 5.0 and 35.0 mg L?1, respectively. A similar trend of increment of ammonia-N, organic-N, phosphate, sulfate and metals in downstream samples was observed. Since the water from these shallow aquifers at both places is not being used for human consumptions or for any other commercial purpose, therefore, the minor increase in pollutants concentration at downstream level is not of a great concern.  相似文献   

6.
Arsenic (As) poisoning of groundwater in Bangladesh has become a major environmental and health issue. The extensive use of groundwater in irrigation of rice has resulted in elevated As in soils and crops. A study was undertaken to determine As concentrations in groundwater, soils, and crops in 16 districts of southwestern Bangladesh. Groundwater samples were collected from shallow-tube and hand-tube wells (STW and HTW) used for irrigation and drinking water. Soil and rice plants were sampled from the command area of the tube wells. Arsenic concentrations were determined using an atomic absorption spectrometer equipped with flow injection hydride generator. Groundwater samples contained <10 to 552 μg As L?1. Arsenic concentrations in 59% of STW samples exceeded 50 μg As L?1, the national standard for As in drinking water. Unlike groundwater, most of the surface water samples contained <10 μg As L?1. Concentrations of As in the soils from the command area of the tube wells ranged from 4.5 to 68 mg kg?1. More than 85% of the soils contained <20 mg As kg?1. The mean As concentration in the rice grain samples was 0.23 mg kg?1, which is much less than the maximum food hygiene standard. A positive relationship was observed between groundwater and soil As, implying that soil As level increases as a result of irrigation with contaminated water. However, irrigation water As did not show any relation with rice grain As. The findings suggest that surface water bodies are a safe source of irrigation water in the As-contaminated areas.  相似文献   

7.
Water samples from 78 private potable wells in southern New Jersey were collected for mercury analysis in 1991–1992. Analyses were performed for the quantification of reactive, volatile and methyl mercury species. Relationships of mercury with other water quality parameters were evaluated also. Total mercury concentrations varied from <1 ng L?1 to over 36 Μg L?1. The dominant forms in which mercury occurred in the wells sampled were Hg? and HgCl2?, although methyl mercury was present in some wells and comprised up to 8% of the total mercury in the ground water samples.  相似文献   

8.
Experimental addition of phosphate to enclosures in an acidified lake in Southern Norway was performed to study the effect on nitrate, pH and labile aluminium along a gradient of phosphate from 4–19 µg P L?1. Nitrate decreased from 180 µg L?1 to below detection limit after three weeks at P-concentrations > 17 µg L?1, due to phytoplankton uptake. pH increased from 4.9 to 5.2, corresponding to a 50% decrease of H+-equivalents from 12 to 6 µg P L?1 due to algal uptake of H+-ions when assimilating NO3 ?-ions. Due to the increased pH and probably also precipitation with phosphate, concentrations of labile aluminium decreased from 150 to 100 µg L?1 within the P-interval 4–19 µg L?1. Algal biomass increased from 0.5 to 6 µg chlorophyll a L?1 along the same P-gradient. The results suggest that moderate P-addition (< 15 µg P L?1 to avoid eutrophication problems) can improve water quality in moderately acidified lakes, and also increase nitrate retention in strongly acidified lakes. In humic lakes, the treatment will be less efficient due to light limitation of primary production and the presence of organic acids.  相似文献   

9.
(pp. 825–831)

This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L?1.

For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg?1 dry soil or higher in the 0–30 cm layer; 38 kg ha?1 of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg?1 dry soil; 75 kg ha?1 of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg?1 dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L?1 from early harvest time to topping time under these conditions.  相似文献   

10.
密云水库流域地下水硝态氮的分布及其影响因素   总被引：10，自引：0，他引：10  
2008年11月至12月,采集了密云水库流域305个井的地下水样品,分析了其硝态氮含量。结果表明,密云水库流域地下水的硝态氮含量的平均值、超标率(10 mg L-1≤NO3--N<20 mg L-1)和严重超标率(NO3--N≥20 mg L-1)分别为6.81 mg L-1、13.77%和2.30%。其中村庄和菜地的地下水硝酸盐污染最为严重,35个村庄井和13个菜地井的地下水硝态氮含量的平均值分别为9.52 mg L-1和9.55 mg L-1,已接近WHO饮用水硝态氮含量10 mg L-1的限定标准,超标率分别为20%和15.38%,严重超标率分别为8.57%和7.69%。219个粮田井水的硝态氮水平位居中间,其硝态氮含量的平均值、超标率和严重超标率分别为6.59mg L-1、14.61%和1.37%。10个林地井的地下水硝态氮含量是最低的,其平均值为2.66 mg L-1,无超标现象。潮河流域农田地下水的硝酸盐污染比白河流域严重。潮河流域农田(124个井)的地下水硝态氮含量的平均值、超标率和严重超标率分别为8.42 mg L-1、21.77%和3.23%,而白河流域(122个井)则分别为5.03mg L-1、6.56%和0,即无严重超标现象。密云水库流域农田地下水的硝态氮含量呈现出上游低而下游高的趋势。玉米田地下水硝态氮含量在接近河道的地方有所降低,与地下水水位呈负相关,与化肥氮的施用量呈正相关,当地下水位小于7m时或当一年的化肥氮的施用量超过200 kg hm-2,存在地下水硝态氮含量超标的潜在危险。  相似文献   

11.
A simple ion chromatographic method is proposed for the simultaneous quantification of five inorganic anions in samples derived from tea system with a suppressed conductivity detector. For this purpose extracts of leaves, roots and soils of tea obtained at room temperature yielded chromatographic profiles with substantial differences in the relative contents of fluoride (F?), chloride (Cl?), nitrate (NO3?) and sulfate (SO4 2-). Although Cl? and SO42- were common to each extracted sample in different categories and accounted for the majority of the anions present, one additional anion peak was detected in root and leaf tissues. Irrespective of the clone and sample investigated the average F? content varied from 253 to 1664 mg kg?1, Cl? varied between 60 and 1789 mg kg?1, NO3? varied from 119 to 188 mg kg?1 and SO42- varied between 55 and 6779 mg kg?1. The anionic load was at its crest in clone UPASI – 3 in all the three categories of samples with few exceptions. Among the samples investigated, tea roots contained a considerable amount of major anions, while tea soils had the lowest amount of the detected anions. The recovery of all the quantified anions was above 95%. The correlation coefficient for all anions where above 99.50%. The concentration of nitrite (NO2?) was below the limits of detection based on the analytical technique adopted. Anion nitrate was not detected in tea root and tea leaf extracts.  相似文献   

12.
Of all groundwater pollution sources, septic systems are the second largest source of groundwater nitrate contamination in USA. This study investigated shallow groundwater (SGW) nutrient dynamics in septic areas at the northern part of the Lower St. Johns River Basin, Florida, USA. Thirty-five SGW-monitoring wells, located at nine different urban areas served by septic systems, were used to collect the SGW samples seasonally and/or biweekly for a duration of 3?years from 2003 to 2006. Analytical results showed that there were 16 wells with nitrate concentrations exceeding the US Environmental Protection Agency's drinking water limit (10?mg?L?1). There also were 11 and 14 wells with total Kjeldahl nitrogen (TKN) and total phosphorus (TP) concentrations, respectively, exceeding the ambient water quality criteria (0.9?mg?L?1 for TKN and 0.04?mg?L?1 for TP) recommended for rivers and streams in nutrient Ecoregion XII (Southeast USA). In general, site variations are much greater than seasonal variations in SGW nutrient concentrations. A negative correlation existed between nitrate/nitrite?Cnitrogen (NOx?CN) and TKN as well as between NOx?CN and ammonium ( $ NH_4^{ + } $ ), whereas a positive correlation occurred between TKN and $ NH_4^{ + } $ . Furthermore, a positive correlation was found between reduction and oxidation (redox) potential and water level, while no correlation was observed between potassium concentration and redox potential. This study demonstrates a need to investigate the potential adverse impacts of SGW nutrients from the septic areas upon the deeper groundwater quality due to the nutrient penetration and upon the surface water quality due to the nutrient discharge.  相似文献   

13.
Quantitative knowledge of background nitrogen (N) concentrations and loadings is essential for as it determines the minimally disturbed conditions for N in surface waters as a near reference condition. To determine background N concentrations, a total of 39 smaller Danish streams draining relatively undisturbed catchments in different regions were selected and screened for N concentrations and discharge during a 1-year period (2004–2005). Only 19 of the streams fulfilled the threshold set for least disturbed conditions (LDC) in their catchments (proportion of agricultural land <10%). Within the five sampled dominant landscape types in Denmark, the concentrations of ammonium N and total organic N in the LDC streams were found to be nearly constant: 0.05 ± 0.01 mg N L?1 and 0.53 ± 0.07 mg N L?1, respectively. In contrast, the concentration of nitrate N differed significantly (P < 0.05) between the five landscape types, with variations between 0.06 and 0.83 mg N L?1. An analysis of all the 39 streams sampled demonstrated significantly different relationships between the proportion of land use and the flow-weighted annual concentration of nitrate N for two dominant soil types with a Y-axis intercept equal to 0.12 mg N L?1 for streams draining coarse textural soils and 0.76 mg N L?1 for streams draining finer textural soils. A significant (P < 0.05) downward trend (18–41%) emerged for flow-weighted annual total N concentrations in four of the five streams that were sampled during the period 1990–2011. A 5 × 5 km grid map of Denmark showing nitrate N and total N background concentrations was produced and used for estimating background N losses to Danish surface waters. Based on the grid map, the average annual background loss of total N was calculated to be 13,000 tonnes N or 19% of the total N loading to Danish coastal waters during the period 2004–2005.  相似文献   

14.
Engineered plant growth media must support plant growth while minimizing environmental impact. The objective of this research was to determine how different growth media influence nutrient leaching. Plant growth media contained varied amounts of soil, sand, compost that did or did not contain manure, and possible sorbents for phosphorus. If the plant growth media included compost derived partly from manure, leaching losses of nutrients were excessive due to the high nutrient load in the compost. Layering compost over the plant media mix resulted in lower nitrate concentrations in effluent (87 mg L?1) compared with mixing compost into the media (343 mg L?1); however, growth of prairie grasses was reduced because of dense media below the compost blanket (0.09 versus 0.31 g). Using lower amounts of compost that did not contain manure resulted in lower mean nitrate concentrations in effluent (101 versus 468 mg L?1). Media that had no soil (13.3 mg L?1) had greater loss of phosphorus after harvest for unsaturated drainage than media with soil (1.8 mg L?1). To reduce nitrate leaching, only small amounts of low-nutrient compost (higher C:N ratio) should be incorporated into the media. If compost is applied as a surface blanket without incorporation, then soil should be added to the sand to reduce density of the media and increase plant growth.  相似文献   

15.
Runoff from a highway interchange in western Maryland had Al concentrations averaging about 50 mg L?1, with a maximum of 206 mg L?1. As an alternative to expensive chemical treatment of this Al-rich water, in August 1984, the drainage was diverted through a 500 m2 man-made wetland, constructed from organic peat. For a 10 week period, Al concentrations in water leaving the wetland averaged 1.5 mg L?1. as compared to Al concentrations at the two major inflows to the wetland of 35.3 and 6.6 mg L?1. However, effective treatment of the drainage by the wetland was not observed over the entire 27 mo sampling period. Peat chemical analysis indicated that over the 27 mo, total Al concentration in the peat increased from 2375 μg g?1 to 13 634 μg g?1. Of this increase 5.5 % was contributed by exchangeable Al, 4.3% by adsorbed Al, 39.8% by organically bound Al, 33.1% by oxide bound Al, and 17.2% by precipitated and residual Al. Changes in Fe, Mn, Ca, Mg, K, and Na chemistry in the peat associated with Al retention are discussed.  相似文献   

16.
This study is aimed at assessing the ability of metal-resistant yeast, Candida tropicalis, to uptake cadmium from the liquid medium. The minimum inhibitory concentration of Cd2+ against C. tropicalis was 2,800 mg L?1. The yeast also showed tolerance towards Zn2+ (3,100 mg L?1), Ni2+ (3,000 mg L?1), Hg2+ (2,400 mg L?1), Cu2+ (2,300 mg L?1), Cr6+ (2,000 mg L?1), and Pb2+ (1,200 mg L?1). The yeast isolate showed typical growth curves, but low specific rate of growth was observed in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 7. The metal processing ability of the isolate was determined in a medium containing 100 mg L?1 of Cd2+. C. tropicalis could decline Cd2+ 57%, 69%, and 80% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd2+ 56% and 73% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and non-protein thiol levels by 146.15% and 59.67% at 100 mg L?1 concentration, respectively. Metal tolerance and accumulation together with changes in the GSH status and non-protein thiols under Cd exposure were studied in C. tropicalis.  相似文献   

17.
ABSTRACT

Influences of nickel (Ni) concentrations in the nutrient solution on yield, quality, and nitrogen (N) metabolism of cucumber plants (Cucumis sativus cv ‘RS189’ and ‘Vikima’) were evaluated when plants were grown either with urea or nitrate as the sole N source. The cucumber plants were treated with two N sources, urea and nitrate as sodium nitrate (NaNO3) at 200 mg L?1, and three concentrations of Ni as nickel sulfate (NiSO4·6H2O; 0, 0.5, and 1 mg L?1). Treatments were arranged in a randomized block design with six replicates. The highest concentration of Ni in the leaves (1.2 mg kg?1 Dwt) was observed in the urea-fed plants at 1 mg L?1 Ni concentration. Additions of Ni up to 0.5 mg L?1 had no effect on the fruit Ni concentration in the both urea and nitrate-fed plants. Yield significantly (p < 0.05) increased with the Ni supplements from 0 to 0.5 mg L?1 (10 and 15% in ‘RS189’ and ‘Vikima’, respectively), but decreased when 1 mg L?1 Ni applied to the solutions in urea-fed plants. Nitrate-fed plants had a higher percentage of total soluble solids compare to those urea-fed plants. Nitrate concentrations of the fruits in urea-fed plants in both cultivars were reduced by approximately 50% compared to those nitrate-fed plants. The reduction of nitrate concentration in the fruits became more pronounced as the Ni concentration increased in the solution. The rate of photosynthesis (Pn) increased with the increase of the Ni concentration in the solution with urea-fed plants. Both N concentration and nitrate reductase (NR) activity of young leaves were higher in urea-fed plants at 0.5 mg l?1 Ni concentration. Ni supplements enhanced the growth and yield of urea-fed plants by increasing Pn, N concentration and NR activity. It can be concluded that Ni supplements (0.5 mg l?1) improve yield, quality, and NR activity in urea-fed cucumber plants.  相似文献   

18.
Subsurface drainage systems have been installed in about 10000 ha of agricultural land in the flat part of the Emilia-Romagna Region in northern Italy. Nitrate loss in drainage water from a representative farm in this area was measured for three consecutive years (1986, 1987, 1988). During this period a total of 369 water samples were collected, filtered at 0.45 µm and analyzed. The nitrate concentration exceeded the limits for surface water set by Italian law regarding water pollution (90 mg NO3 ?L?1 = 20 mg N L?1) in 84% of the samples. The greatest nitrate loss was recorded during the winter and early spring when drainage was high. After this period loss of nitrate, via drainage water, progressively decreased. This was attributed to a decrease in the amount of drainage water and increase in crop uptake of N. The average annual nitrate loss via drainage water was around 200 kg of NO inf3 sup? ha?1. Annual nitrate losses of this order of magnitude (? 50 kg N ha?1) indicate an urgent need for implementation of management practices directed towards achieving considerable reductions in these losses.  相似文献   

19.
RDX was not acutely toxic to the green alga Selenastrum capricornutum when tested at the solubility limit of the compound in algal assay media. A maximum reduction of 38% in cell density occurred after a 96-h exposure to 36.7 mg L?1; thus, an EC50 could not be determined. The lowest-observed-effect concentration (LOEC) and no-observed-effect concentration (NOEC) for the green alga were 4.8 and 0.5 mg L?1 (reduction in cell density), respectively, when chronic end points were used to analyze the data. A comparison of the data in this study with RDX toxicity data from the literature for the diatom Navicula pelliculosa, and the blue-green algae (cyanobacteria) Microcystis aeruginosa and Anabeana flos-aquae shows that S. capricornutum is the most sensitive to RDX. A U.S. Environmental Protection Agency (EPA) numerical water quality criterion Final Plant Value based on the green alga data should protect the above algal groups.  相似文献   

20.
Taking Cd as an example we introduce a procedure to estimate tolerable total content of heavy metals in soils with regard to a specific ground water quality criterion. Furthermore, we present a piston‐flow approach to estimate breakthrough times of a sorptive solute to the ground water. Both procedures are applied to the sandy soils in the 4300 ha wastewater irrigation area Braunschweig, Germany. Applicability of these procedures is tested by numerical simulations. The calculated breakthrough times of Cd for an input concentration of 3 μg L−1 and a mean water flux density of 570 mm yr−1 varies, as a function of depth of water table and sorption characteristics, between 10 and 805 years (mean = 141 years). The deviation between the piston‐flow approach and the numerical simulation is on the average 1.6%. We determined a mean tolerable total Cd content of 0.61 mg kg−1 with regard to a ground water quality criterion of 3 μg L−1. The limit of the German sewage sludge regulation (AbfKlärV, 1992) of 1 mg Cd kg−1 exceeds the calculated tolerable total content in 90% of the investigated Ap horizons. Moreover, the results of the numerical simulations show that the limit of 1 mg Cd kg−1 would lead to a concentration in seepage water significantly above 8 μg Cd L−1. We conclude that in the sandy soils of the wastewater irrigation area the current limit of 1 mg Cd kg−1 is not sufficient to keep the Cd concentration in seepage water below 3 μg L−1 and, thus, to ensure ground water protection in the long run.  相似文献   

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