Evaluation of wastewater reclamation technologies based on in vitro and in vivo bioassays

When municipal secondary effluent is used as the main supplementation water source for surface water bodies, its potential adverse ecological effects should not be neglected. The objective of this work was to investigate the effectiveness of several technologies, i.e. combination of coagulation and sand filtration (CSF), ultraviolet (UV) irradiation, chlorination, ozonation, ultrafiltration (UF) and reverse osmosis filtration (RO), on the removal of acute ecotoxicity, genotoxicity and retinoic acid receptor (RAR) agonist activity from the municipal secondary effluent. The effects of treated effluents on the development of Japanese medaka (Oryzias latipes) embryos were also evaluated. The secondary effluent exhibited a mutagenic effect on Salmonella typhimurium strain TA 1535/pSK1002, acute invertebrate toxicity to Daphnia magna, and weak RAR α activity. RO and ozonation demonstrated remarkable removals of the genotoxic effect, acute toxicity and RAR activity from secondary effluent, while chlorination could elevate both genotoxicity and acute toxicity. CSF, UV, UF, chlorination as well as RO could decrease the 4-day mortality of medaka embryos and accordingly increase the hatching success rate, comparing with the secondary effluent. Ozonation at 4 mg/l and higher doses, however, elicited significantly higher 4-day mortality, leading to the reduction of the hatching success rate.     

Quantitative assessment of estrogenic activity in the water environment of Korea by the E-SCREEN assay

In this study, the E-SCREEN assay was optimized and validated for the sensitive quantitative determination of the total estrogenicity in river samples. River water and sediment samples were collected and analyzed with the E-SCREEN. River water (10 l) was extracted using combined solid-phase extraction in static adsorption mode with Soxhlet extraction. Estrogenic pollutants adsorbed to the XAD-4 resin were recovered with 98.24 +/- 5.90% efficiency by elution with ethyl acetate and dichloromethane (1:9). The detection limit by 17beta-estradiol equivalent concentration (EEQ) of the E-SCREEN assay was 8.03 pg EEQ/l. Among the water samples, the estrogenic activity was observed to be higher downstream of the Kumho river (7.43 ng EEQ/l) and upstream of Kum river (2.05 ng EEQ/l) than in other samples. More than 3 mg of equivalent sediment samples from the Kumho river, Kum river and Miho stream showed partial agonistic effects, and the Mankyung river showed a partial agonistic effect with only 1.5 mg of sediment. The highest value of RPE was 83.34 downstream of the Kumho river, and the lowest value of RPE was 6.52 downstream of the Miho stream. Full estrogen agonistic activities were observed downstream of the Kumho river and upstream of the Kum river. The partial agonistic activity was observed in upstream of the Kumho river, downstream of the Mankyung river, and upstream of the Miho stream, and no agonistic action was observed downstream of the Kum river or Miho stream, or upstream of the Mankyung river. The total estrogenic activity in the river water and sediment samples was between 0.50 pg/L and 7.4 ng/L, 3.39 pg/g and 10.70 pg/g.     

Identification of estrogen-like effects and biologically active compounds in river water using bioassays and chemical analysis

The Nackdong River is the longest river in South Korea and passes through major cities that have several industrial complexes, including chemical, electric, and petrochemical complexes, and municipal characteristics such as apartment complexes. Along the river, the Gumi region has an electric industrial complex and an apartment complex that may be possible point sources of xenoestrogens such as phenolic compounds. To identify the causative chemicals for estrogenic activity in the river water of this region, bioassay-directed chemical analysis was performed. All samples from six sampling sites (an upstream point: S1; hot spot points: S2-1, S2-2, and S2-3; and downstream points: S3, and S4) showed estrogenic activity in the E-screen assay, with bio-EEQs (17β-E₂-equivalent quantities) ranging from 25.35-677.15 pg/L. Samples from S2-2, the sampling point downstream of the junction of stream water, and domestic and industrial wastewater, contained the highest estrogenic activity. Since the bio-EEQ of the organic acid fraction (F2) of the S2-2 sample had the highest activity (823.25 pg-EEQ/L) and F2 may contain phenolic compounds, GC-MS analyses for phenolic xenoestrogens were conducted with the organic acid fractions of the river water samples. Six estrogenic phenolic chemicals, 4-NP, BPA, 4-t-OP, 4-t-BP, 4-n-OP, and 4-n-HTP, were detected, with the highest concentrations (I-EEQ) found in S2-2 (231.80 pg/L). Among these phenolic chemicals, 4-NP was the most potent estrogen (bio-EEF; 8.12 × 10^− 5) and acted as a full agonist. Furthermore, 4-NP was present at levels (2.0 µg/L in S2-2) that can induce VTG induction in fish (>1 µg/L). In addition, we confirmed that river water (S2-2) significantly increased serum VTG levels in crucian carp (Carassius auratus) in a fish exposure experiment under laboratory conditions. Therefore, phenolic xenoestrogens, especially 4-NP, may be the main causative compounds responsible for the estrogenic effect on the Nackdong River.     

Assessment of river contamination by estrogenic compounds in Paris area (France)

Wastewater treatment plants (WWTPs) receive a large spectrum of endocrine disrupting compounds (EDCs) that are partially eliminated during treatment processes and discharged into rivers. Given the lack of information in France about river contamination by EDCs, we chose to examine estrogenic potential of WWTP influents, effluents and receiving waters in Paris and its suburbs. Water samples were analyzed using gas chromatography coupled with mass spectrometry for quantifying natural and synthetic estrogens combined with an in vitro estrogenicity bioassay associated to a high pressure liquid chromatography fractionation. The four estrogens investigated, Estrone (E1), 17beta-Estradiol (E2), Estriol (E3) and 17alpha-Ethinylestradiol (EE2) were found in all WWTP and river samples at concentrations ranging from 2.7 to 17.6 ng/l and 1.0 to 3.2 ng/l, respectively. The synthetic estrogen EE2 seems more resistant to biodegradation in WWTPs and thus accounted for 35-50% of the estimated estrogenic activity in rivers. However, fractionation of samples and differences between concentrations of E1, E2, E3 and EE2 and the estrogenic activity measured by the in vitro bioassay suggested a complexity of mechanisms underlying the biological response that could not be attributed only to the investigated molecules.     

Concentration and loading of pesticide residues in Lake Biwa basin (Japan).

The concentrations and loading rates of pesticides used in paddy fields were investigated over a period of 5 years in the Seta River, which is the only natural outlet of Lake Biwa. The lake's water catchment area is 3,174 km2, 20% of which contains paddy fields. Water samples were also collected in six rivers flowing into the lake in order to compare the contamination level and concentration profile. The pesticides analyzed were four herbicides (molinate, simetryn, oxadiazon, and thiobencarb), one fungicide (isoprothiolane), and two insecticides (diazinon and fenitrothion). Molinate, simetryn, oxadiazon and isoprothiolane were found at the higher frequencies with maximum concentrations of 1.1, 0.4, 0.1 and 0.5 microg,/l in the effluent river, one or two order of magnitude higher than that of effluent in influent rivers. These peak concentrations were observed during the application period in influent rivers and two or three weeks after that in effluent river. The frequency of occurrence of thiobencarb, diazinon, and fenitrothion was relatively low and their maximum concentrations in the effluent remained below 0.1 microg/l. The decrease of molinate, simetryn and oxadiazon concentrations in the effluent river were approximated by two straight lines plotted on semilogarithmic scale. Increased loading was induced by intense rainfall, which took place during the application period. Simetryn and isoprothiolane persisted in relatively high concentrations through the year were also influenced on its loading by the heavy rainfall in the following months. The percentages of the total amount of pesticides released through Lake Biwa to the basin in downstream were estimated to be 1.3-2.9% for molinate, 5.4-10.0% for simetryn, 0.6-1.3% for oxadiazon, 0.2-0.9% for thiobencarb, 1.8-6.6% for isoprothiolane, 0.3-2.1% for diazinon. and 0% for fenitrothion.     

Levels of DDT and hexachlorocyclohexane in burbot (Lota lota l.) from Russian Arctic rivers

The concentrations of organochlorine pesticides (OCPs =p,p'DDT, p,p'DDD, p,p'DDE, alpha-HCH and gamma-HCH) were measured in the sediments, water and burbot (whole liver and liver lipids) of eight Russian Arctic rivers near their outflows to the Arctic Ocean between 1988 and 1994. DDT was not detected in any river sediments above the limit of quantification (LOQ) of 2.5 ng g(-1) dry wt. Concentrations of DDD and DDE were only found in three of the river sediments above the LOQ of 0.75 ng g(-1) dry wt. DDT and DDE were present in only North Dvina and Pechora river water above the LOQ of 5 ng l(-1), while DDD was not found in any river above this limit. Both alpha- and gamma-HCH were found in all river sediments except for the Kolyma River at concentrations up to 2.4 and 3.5 ng g(-1) dry wt., respectively. In river water, alpha-HCH was as high as 8.6 ng l(-1) in the Ob River and gamma-HCH as high as 7.6 ng l(-1) in the Pechora River. The concentration of both sigmaDDT and sigmaHCH decreased to LOQ levels by about 1992 in both water and sediments. sigmaDDT (up to 70 ng g(-1) wet wt.) and sigmaHCH (maximum 18 ng g(-1) wet wt.) in burbot livers followed a similar temporal trend as in water and sediments. There is a scarcity of OCP data for Russia, but from what is available, we conclude that: (1) contamination of Russian rivers and burbot by OCPs is less severe in the Arctic than at lower latitudes; (2) contamination of Russian Arctic burbot is comparable to, or lower than, similar OCP contamination measured in burbot and other fish in other countries; and (3) the OCP concentrations in Russian burbot pose a negligible health risk to either humans or wildlife.     

Sulfur and strontium isotope geochemistry of tributary rivers of Lake Biwa: implications for human impact on the decadal change of lake water quality

To study the deterioration of the water quality in Lake Biwa, Japan, over the last 40 years, we measured the concentrations and isotopic ratios of sulfur and strontium of water in 41 inflowing rivers and one discharging river. The concentrations of SO4 and Sr of inflowing rivers at downstream sites were generally high in the southern urban area and in the eastern area, where a large agricultural plain is situated, but low in the northern and western areas, whose watersheds are mountainous and with low population density. SO4 and Sr concentrations are also lower at upstream sites, which are closer to mountainous areas. Thus, the inflowing river receives large amounts of SO4 and Sr as it flows across the plain, where human activity levels are high. The delta34S or 87Sr/86Sr values of most eastern rivers at downstream sites are lower than those of water in Lake Biwa, and values become more uniform as the proportion of the plain area in the watershed increases. River water in other areas has higher values of delta34S or 87Sr/86Sr than the lake water. This result indicates that the decadal decrease of delta34S and 87Sr/86Sr in the lake water has been caused mainly by the increased flux of SO4 and Sr from rivers in the eastern plain. We assume that in the plain, sulfur, nitrogen, and organic compounds induced by human activities generate sulfuric, nitric, and organic acids in the water, which accelerate the extraction of Sr from bedrocks, leading to the generation of Sr in the river water in the area.     

Persistent organic pollutants in fish tissue in the mid-continental great rivers of the United States

Great rivers of the central United States (Upper Mississippi, Missouri, and Ohio rivers) are valuable economic and cultural resources, yet until recently their ecological condition has not been well quantified. In 2004-2005, as part of the Environmental Monitoring and Assessment Program for Great River Ecosystems (EMAP-GRE), we measured legacy organochlorines (OCs) (pesticides and polychlorinated biphenyls, PCBs) and emerging compounds (polybrominated diphenyl ethers, PBDEs) in whole fish to estimate human and wildlife exposure risks from fish consumption. PCBs, PBDEs, chlordane, dieldrin and dichlorodiphenyltrichloroethane (DDT) were detected in most samples across all rivers, and hexachlorobenzene was detected in most Ohio River samples. Concentrations were highest in the Ohio River, followed by the Mississippi and Missouri Rivers, respectively. Dieldrin and PCBs posed the greatest risk to humans. Their concentrations exceeded human screening values for cancer risk in 27-54% and 16-98% of river km, respectively. Chlordane exceeded wildlife risk values for kingfisher in 11-96% of river km. PBDE concentrations were highest in large fish in the Missouri and Ohio Rivers (mean > 1000 ng g^− 1 lipid), with congener 47 most prevalent. OC and PBDE concentrations were positively related to fish size, lipid content, trophic guild, and proximity to urban areas. Contamination of fishes by OCs is widespread among great rivers, although exposure risks appear to be more localized and limited in scope. As an indicator of ecological condition, fish tissue contamination contributes to the overall assessment of great river ecosystems in the U.S.     

Identification of estrogen receptor agonists in sediments from Wenyu River, Beijing, China

Assignment of ecological impacts of contamination to specific classes of contaminants is a prerequisite for risk assessment and remediation. In this study, the combination of polarity-based fractionation, two-hybrid yeast bioassay, and chemical analysis were used to evaluate and identify estrogen receptor agonists (ER-agonists) in sediments from Wenyu River, Beijing, China. By bioassay, organic raw sediment extracts could induce significant estrogenicity and the bioassay-derived 17β-estradiol equivalents (EEQs) of raw extracts (EEQ_raws) ranged from 0.8 to 19.8 ng/g dry weight. By polarity-based fractionation, the raw extracts were separated into three fractions, i.e. non-polar, moderately polar, and polar fractions, which were subjected to bioassay and chemical analysis. The highest estrogenicity was observed in the polar fraction, which accounted for more than 78% of the total. The medium polar fraction contains PAHs and OCPs, and the estrogenic activities in this fraction contributed 3%-12% of the total in raw extract. An estrogenic activity of non-polarity fraction was negligible in compare to other two fractions. By chemical analysis and toxic equivalent calculation, major part of the estrogenicity in polar fraction could be attributed to six natural/synthetic estrogens (16%-63%), i.e. 17β-estradiol, estrone, estriol, 17α-ethynylestradiol, diethylstilbestrol, and β-estradiol-17-valerate, and to nonylphenols (26%-55%). The proposed approach has been successfully used for characterization of ER-agonists in this case study.     

Contribution of known endocrine disrupting substances to the estrogenic activity in Tama River water samples from Japan using instrumental analysis and in vitro reporter gene assay

To quantitatively characterize the substances contributing to estrogenic activity in river water, in vitro bioassay using MVLN cells and instrumental analysis using liquid chromatograph–mass spectrometer (LC/MS) or liquid chromatograph–tandem mass spectrometer (LC/MS/MS) were applied to river water extracts taken from various locations in the Tama River, Japan. Tama River water samples were extracted using solid phase extraction and the crude extracts were fractionated by high-performance liquid chromatography (HPLC) into 10 fractions. The sixth fraction contained nonylphenol (NP) and octylphenol (OP) at concentrations in the range of 51.6–147 and 6.9–81.9 ng/L, respectively (concentrations corresponding to the original sample volumes). No estrogenic activity, expressed as 17β-estradiol equivalents (E2-EQ_B), however, was observed in this fraction (<0.6 ng-E2eq/L). Instrumentally determined estrogenic activity (E2-EQ_C), which is the concentrations of NP and OP multiplied by their corresponding relative potency, was below the detection limit of the MVLN cell bioassay. Estrogenic activities were detected only in HPLC fraction nos. 7, 8 and 9. Estrone (E1), estradiol (E2) and bisphenol A (BPA) were detected in these fractions. Estriol (E3) and ethynylestradiol (EE2) were not detected (<0.2 ng/L) in these fractions. The calculated E2-EQ_C for BPA was below the detection limit of bioassay. The E2-EQ_C for E1 and E2 were on the same order as the estrogenic activity determined by the bioassay (E2-EQ_B). The ratios of E2-EQ_C and E2-EQ_B for E1 and E2 in the three factions collectively (nos. 7–9) were 0.49–0.97 and 0.29–1.12, respectively. Above results indicated that the major causal substances to the estrogenic activity in the Tama River were E1 and E2.     

Combination of in vitro bioassays encompassing different mechanisms to determine the endocrine-disrupting effects of river water

In this study, the total toxic effects of river water samples were assessed using a series of cell culture bioassays which encompassed different mechanisms, based on specific modes of action. River water samples were collected from three tributaries of the Youngsan River in the western portion of Korea. We confirmed that Youngsan River water was polluted with a complex mixture of estrogenic and dioxin-like compounds. The total toxic effects of the downstream water samples were found to be higher than that of the upstream water samples. In the upstream water samples, total estrogenic activity was measured to be between 0.005 and 0.049 ng-EEQ/l (17beta-estradiol-equivalent concentration) and no CYP1A activity was detected. In the downstream water samples, however, total estrogenic activity was measured to be between 0.021 ng-EEQ/l and 1.918 ng-EEQ/l, and total CYP1A activity was between 0.63 and 3.55 microg-MEQ/l (3-methylcholanthrene-equivalent concentration). When assessed according to a concentration-response curve, downstream water sample extracts exerted dual actions on estrogen receptors, depending on the concentration volume of the samples. The concentration volume range proximal to the original water sample exhibited estrogenic activity, whereas antiestrogenic activity was observed at high concentration volumes (more than 5 times concentration) in the extracts. This study involved a combination of in vitro bioassays, designed to encompass different mechanisms. The bioassays used included the estrogen receptor binding affinity test, E-screen assay, aromatase assay, and EROD assay. These tests provided a great deal of useful information regarding the potency and action modes of estrogenicity and antiestrogenicity inherent in the sampled river water. Although further study is necessary to determine the relationship between toxic responses in in vitro bioassay systems and chronic toxicity in aquatic organisms, our approach is expected to be fairly accurate with regard to the detection of endocrine-disrupting effects in an aquatic environment.     

Plasma vitellogenin levels and gonadal morphology of wild carp (Cyprinus carpio L.) in a receiving rivers downstream of sewage treatment plants

A field study was carried out in order to assess, in a wild cyprinid fish, the biological effects related to the exposure to estrogenic compounds. The gonadosomic index (GSI), plasma vitellogenin (VTG) level and histological observations of gonads were performed to evaluate the reproductive health in common carp (Cyprinus carpio) from three rivers receiving sewage treatment plant (STP) effluents (Guadarrama, Henares and Jarama rivers, Spain) and from a reference site (Lozoya river). No significative differences in male GSI between sites were described. Only in the 18% of fish from Guadarrama river were elevated plasma VTG levels detected. The presence of oocytes in the testis was not found in any of males examined. The results suggest that the released estrogenic compounds by STPs effluents are not enough capable to adversely affect the gonadal development of the fish studied. Additional studies will be required to assess the risk of estrogenic compounds on fish from other sites of this area.     

Herbicide, CNP contamination in the Lake Kasumigaura basin

Environmental contamination by CNP was investigated in Lake Kasumigaura and the Sakura River. The residual concentrations of free nitro-, free amino- and total-CNP were determined by gas chromatography with an electron capture detector. Free nitro-CNP was found, at ppt level, in the Sakura River water in May and June. Though CNP in the river water disappeared quickly, it persisted in paddy field soil, lake and river sediment, and fish and shellfish long after its application. The concentrations of free nitro- and amino-CNP in paddy field soil and river sediment were much lower than those of total-CNP. CNP was found to maintain a wide distribution throughout the aquatic environment, not only as nitro-CNP but also as amino-CNP and other derivatives. The half-life of total-CNP was about 3 years in the lake sediment.     

迈阿密河绿道一条工业河流的绿色基础设施

迈阿密河是美国最短城市河流之一,同时也是佛罗里达州南部最古老的天然地标。迈阿密的意思是"甘甜的水",2500年以来迈阿密河一直是从沼泽地到比斯坎湾的淡水出水口。直到20世纪40年代,河流仍然主要呈自然状态。二战期间河流为船只生产制造业发挥了重要作用,而现如今沿河的使用主要面向海洋工业活动和国际航运。在过去30年里,社区领导和居民们已计划将河流从工业资源转变成为充满活力的社会资产。绿道公司被委托为"迈阿密河绿色行动计划"制定规划。计划进一步提高了河道的可达性和实用性,使其更好为企业、居民和游客服务;同时也促进了海洋工业活动的繁荣发展,提高了土地价值。此外,新增加的娱乐设施使得河流成为目的地景观。迈阿密的自然和文化遗产得到保护和改善,让子孙后代也能从中受惠。     

Detection of estrogenic activity in sediment-associated compounds using in vitro reporter gene assays

Sediments may be the ultimate sink for persistent (xeno-)estrogenic compounds released into the aquatic environment. Sediment-associated estrogenic potency was measured with an estrogen receptor-mediated luciferase reporter gene (ER-CALUX) assay and compared with a recombinant yeast screen. The ER-CALUX assay was more sensitive to 17beta-estradiol (E2) than the recombinant yeast screen, with an EC50 of 6 pM E2 compared to 100 pM in the yeast screen. Yeast cells were unable to distinguish the anti-estrogens ICI 182,780 and (4-hydroxy)tamoxifen, which were agonistic in the yeast. Acetone-soluble fractions of hexane/acetone extracts of sediments showed higher estrogenic potency than hexane-soluble extracts in the ER-CALUX assay. Sediments obtained from industrialized areas such as the Port of Rotterdam showed the highest estrogenic potency of the 12 marine sediments tested (up to 40 pmol estradiol equivalents per gram sediment). The estrogenic activity of individual chemicals that can be found in sediments including: alkylphenol ethoxylates and carboxylates; phthalates; and pesticides, was tested. Increasing sidechain length of various nonylphenol ethoxylates resulted in decreased estrogenic activity. Of the phthalates tested, butylbenzylphthalate was the most estrogenic, though with a potency approximately 100,000 times less than E2. The organochlorine herbicides atrazine and simazine failed to induce reporter gene activity. As metabolic activation may be required to induce estrogenic activity, a metabolic transformation step was added to the ER-CALUX assay using incubation of compounds with liver microsomes obtained from PCB-treated rats. Results indicate that metabolites of E2, NP and bisphenol A were less active than the parent compounds, while metabolites of methoxychlor were more estrogenic following microsomal incubations.     

Water and sediment transport mechanisms in a large river‐connected lake

Using the finite volume method, a 2‐D water‐sediment coupled model was developed to investigate the transport mechanisms of water and sediment in Poyang Lake, the largest river‐connected lake in China. Simulating water and sediment transport processes in an average water year revealed that the total volume of water and the amount of suspended sediment transported from the five main rivers upstream of Poyang Lake were approximately 1.56 × 10¹¹ m³ and 1.25 × 10⁷ t, respectively. The outputs of water and sediment from the lake to the downstream Yangtze River were approximately 2.17 × 10¹¹ m³ and 1.53 × 10⁷ t, respectively. During the wet season, especially between July and September, nearly 1.06 × 10¹⁰ m³ of water and 1.89 × 10⁶ t of suspended sediment were transported upstream from the Yangtze River into the lake due to the high external water levels, which accounted for 4.88% and 12.35%, respectively, of the total annual transport from the lake into the Yangtze River.     

滨江路对重庆两江水流条件影响的研究

滨江路工程对于发展城市建设和缓解交通运输具有重要意义。但是同时,它也会给河道的水流条件带来变化,从而引起河流的水安全问题、泥沙冲淤问题、航道运输问题等。本文以重庆滨江路工程和长江、嘉陵江汇流河段为对象,对滨江路给河道水流条件带来的变化进行研究,建立了两江汇流数学模型,通过计算机数值模拟,对比滨江路修建前后的河流水位和流场变化情况,阐明了引起这些变化的相关因素及其后果。     

长江与黄河两大流域水生态问题剖析

对流域水生态的研究由传统单一的水质评价逐渐转变为河流生态质量的评价,基于河流健康保障的流域生态保护与发展已成为国际性趋势。长江、黄河两大流域内的生态保护与发展也是重大国家战略。以长江、黄河两大流域为研究对象,对两大流域水生态环境问题进行分区概述,并从河流湖库问题治理的关键是注重流域的整体性的角度,分析为维系两大流域水生态健康可开展的研究工作,最后将生态修复与景观设计结合考虑,提出注重景观价值的流域生态保护策略。     

邯郸市两河综合整治规划与环境保护探析

以邯郸市两河(滏阳河和沁河)综合整治规划为例,阐述了城市内河综合整治应考虑的诸要素,强调指出城市河流综合整治有别于传统意义上的河道整治,需多专业配合与协作。     

Schutz flussnaher Trinkwasserfassungen bei Flussraum-Aufweitungen in voralpinen Schotterebenen

In alpine and peri-alpine flood plains, rivers can lose water to the ground water (infiltrating conditions), or gain water from it (exfiltrating conditions). Since sediments within these flood plains are highly permeable, drinking water wells near infiltrating rivers are often highly efficient. To reduce flood risks, engineers couple hydraulic flood protection measures with an enhancement of lateral connectivity. Eventually, the residence time of the infiltrating ground water is reduced and the fraction of infiltrated water rises. Floods lead to the breakthrough of freshly infiltrated water. This can lead to groundwater contamination, if the river is loaded with wastewater. Where measures of hydraulic engineering are necessary, drinking-water wells must therefore be protected from contamination. We discuss three cases of contamination risk: i) low risk under exfiltrating conditions or where river and ground water interaction is weak, ii) increased risk during or after hydraulic operations under infiltration conditions; and iii) generally high risk at wells with low residence times and high fractions of infiltration water. We suggest that the risk is reduced when a thick unsaturated zone separates the river from the well (> 10?m), compared to direct water loss through saturated media. For wells at risk, we propose technical protection measures to reduce the danger.