Schweizer et al. Environ Sci Eur (2018) 30:22 https://doi.org/10.1186/s12302-018-0150-4 RESEARCH Open Access The importance of sediments in ecological quality assessment of stream headwaters: embryotoxicity along the Nidda River and its tributaries in Central Hesse, Germany Mona Schweizer1* , Andreas Dieterich1, Núria Corral Morillas1,2, Carla Dewald1, Lukas Miksch1, Sara Nelson1, Arne Wick3, Rita Triebskorn1,4 and Heinz‑R. Köhler1 Abstract Background: Although the crucial importance of sediments in aquatic systems is well-known, sediments are often neglected as a factor in the evaluation of water quality assessment. To support and extend previous work in that feld, this study was conducted to assess the impact of surface water and sediment on fsh embryos in the case of a highly anthropogenically infuenced river catchment in Central Hesse, Germany. Results: The results of 96 h post fertilisation fsh embryo toxicity test with Danio rerio (according to OECD Guide‑ line 236) revealed that river samples comprising both water and sediment exert pivotal efects in embryos, whereas surface water alone did not. The most prominent reactions were developmental delays and, to some extent, malfor‑ mations of embryos. Developmental delays occurred at rates up to 100% in single runs. Malformation rates ranged mainly below 10% and never exceeded 25%. Conclusion: A clear relationship between anthropogenic point sources and detected efects could not be estab‑ lished. However, the study illustrates the critical condition of the entire river system with respect to embryotoxic potentials present even at the most upstream test sites. In addition, the study stresses the necessity to take into account sediments for the evaluation of ecosystem health in industrialised areas. Keywords: FET, Sediment toxicity, Ecosystem health, Anthropogenic impacts Background Directive (2000/60/EC) surface waters were supposed Tis study was conducted within the joint project Nid- to be in a good ecological state until 2015. As it is well- daMan, which focused on diagnosis of ecosystem health known, however, that many of those German water bod- in the catchment of the Nidda River in Hesse, Germany, ies had fallen far short of this goal, therefore, the stated as a scientifc basis for river management. Te Nidda period was prolonged until 2027. In Germany, only 7.9% catchment, including the Nidda River and its tributaries of surface waters achieved a ‘good’ and just 0.3% a ‘very Horlof and Usa, can be regarded as a model for medium- good’ ecological state at the frst deadline in 2015 [1]. Te sized stream systems infuenced by intense industrial ecological status assessment is based on two main pillars: and agricultural activity in modern industrialised coun- physicochemical parameters and biological monitoring. tries. With regard to the European Water Framework Physicochemical parameters can be measured continu- ously with relatively little efort. Data obtained are col- lated with existing environmental quality standards *Correspondence: [email protected] (EQS) but also may contribute to deriving new EQS for 1 Animal Physiological Ecology, Eberhard Karls University of Tübingen, Auf Der Morgenstelle 5, 72076 Tübingen, Germany substances uncovered, yet. Te clearest shortcoming of Full list of author information is available at the end of the article chemical analyses is that only substances tested for can © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat​iveco​mmons​.org/licen​ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Schweizer et al. Environ Sci Eur (2018) 30:22 Page 2 of 18 be detected and quantifed. But thousands of substances by waste water treatment plants (in the following abbre- enter our waterbodies on a daily basis, and in the Euro- viated with WWTP) and industrial discharges, as well pean Union alone, thousands of new ones are registered as by agriculture and renaturation measures. Te Nidda in REACH [Regulation (EC) No. 1907/2006 concerning has its source in the Vogelsberg, a low mountain range the Registration, Evaluation, Authorisation and Restric- of volcanic origin in East Hesse, and enters the River tion of Chemicals] every year. Tus, analyses of chemi- Main near Frankfurt. With a length of 89.7 km, the Nidda cal compounds in surface waters are restricted to lead counts among the most important water bodies in Hesse. substances that can only give a scattered picture of the Along its course, agriculture prevails but also grassland, actual situation. Biological monitoring, in contrast, ofers settlements and industry occurs, whereas the fraction of a clear snapshot of the situation in reality, but is time uncultivated land is rather small and, therefore, the entire consuming and cost-intensive. Terefore, biomonitoring catchment is characterised by very intense land-use [17]. is conducted less frequently including a lower number of investigated sites. But even if biomonitoring is repeated Sampling sites in shorter intervals at more sites, the context between Te 14 main sampling sites from a frst and the 16 addi- chemical measurements and status quo of biota in the tional sampling sites from a second sampling campaign feld will still be lacking. Efect-based bioassays and bio- are illustrated in Fig. 1. Te sampling sites N1 and H2 marker are able to bridge that gap because they refect were sampled in both sampling campaigns. the ecotoxicological potential of the studied system, may From the most upstream sampling site (N1) down- be conducted on diferent levels (cells, organs, organisms) stream the River Nidda dam as far as the most down- and are fnancially feasible. As a consequence, the idea of stream sampling site (N6) northeast of Karben discharges complementing the European Water Framework Direc- of four communal WWTPs ranging in size from 7000 to tive (WFD) with additional biotests gains proponents in 35,000 people equivalents (pe) and one in-house purif- the scientifc community, in recent years (e.g. [2–5]). cation plant (industrial discharger) enter the river. Size Te WFD mainly focusses on water quality but as a classifcation of WWTPs in Germany is determined as major driver in the source–sink dynamics of surface followed: class-I < 1000 pe, class-II 1000–5000 pe, class- water systems, the infuence of sediments has to be con- III 5001–10,000 pe, class-IV 10,001–100,000 pe and sidered necessarily [6, 7]. Otherwise, analyses will lead to class-V > 100,000 pe. Additionally, between the fourth false evaluations of the ecotoxicological potential of those (N4) and ffth (N5) sampling site, the Horlof fows into systems [8–12] and therefore, impair the achievement the Nidda and with it discharges from several class-I of the ecological goals set by the WFD [13]. In particu- WWTPs with less than 1000 pe located upstream and a lar, fsh are dependent on sediments during their entire class-IV WWTP covering 78,000 pe in the middle course. embryonic and larval development. Sediments serve as Besides the impact from those WWTPs, the Horlof is spawning substrate and thus, have the potential to infu- particularly infuenced by agriculture. Downstream the ence reproductive behaviour, hatching success, develop- class-IV WWTP, renaturation eforts have been made mental processes and growth [14]. and are to be continued. Upstream of N6, the Usa/Wetter Te objective of this study was to evaluate develop- system enters the Nidda. Along its course, three WWTPs mental toxicity of native river samples on fsh embryos. and several (medical) spas discharge into the Usa and, To account for the efects that may be induced by parti- subsequently, into the Nidda. Te sampling sites at the cle bound substances accumulating in sediments, fsh River Nidda system were set to monitor efects of difer- embryos were exposed to samples, either containing sur- ent sized and equipped WWTPs (N3, N4, N5, N6, H2, face water only or surface water in combination with sed- H3, U2, U4), as well as the impact of special industrial iment from the respective feld sites. Te tests covered dischargers [N2; U3: (medical) spas], but also the poten- lethal as well as sublethal endpoints and were conducted tial positive infuence of renaturation eforts (N6, H4, U3) with the zebrafsh (Danio rerio [Hamilton 1822]) due to (see also Table 1). Te most upstream site of each river its simple handling, lack of a particular spawning season [N1, H1, U1] was originally thought to act as reference, and the standardised test procedure (see e.g. [15, 16]). respectively (see Fig. 1). In addition, in a second sampling campaign three dis- Methods charge areas were examined in greater detail. For that Sampling location purpose, fve sampling sites were set: one upstream the Te River Nidda and its tributaries Horlof and Usa are discharger, one at the point of discharge and the fol- located in Central Hesse, Germany. Tey can be regarded lowing three in approximately similar distances down- as a very characteristic catchment system for Central stream, whereas the length of the transects depended Europe as they are highly anthropogenically infuenced on the accessibility of the river banks. Te decision Schweizer et al. Environ Sci Eur (2018) 30:22 Page 3 of 18 Fig. 1 Map of the sampling area in Central Hesse, Germany including locations of sampling sites and their evaluation based on the percentage of signifcant endpoints compared to control treatments, as well as prominent points of discharge. Round tags mark the main sampling sites, square tags the additional sites, including the samples taken from the efux pipes (DE), the basin (B) and the zone of efuent and river mixture (F) on which sampling sites to choose for a more detailed the last class-I WWTP at H2 was monitored in greater examination was based on results from the frst sam- detail.