What Works? the Influence of Changing Wastewater Treatment Type, Including Tertiary Granular Activated Charcoal, on Downstream Macroinvertebrate Biodiversity Over Time

Potential effects of the discharge of wastewater treatment plant (WWTP) effluents in benthic communities: evidence from three distinct WWTP systems

Wastewater treatment plant (WWTP) effluents can be sources of environmental contamination. In this study, we aimed to understand whether effluents of three different WWTPs may have ecological effects in riverine recipient ecosystems. To achieve this, we assessed benthic phytobenthos and macroinvertebrate communities at three different locations relative to the effluent discharge: immediately upstream, immediately downstream and 500-m downstream the effluent discharge. Two approaches were employed: the ecological status classification as defined in the Water Framework Directive (WFD) based on biological indicators; constrained multivariate analysis to disentangle the environmental drivers (physicochemical variables and contaminants, namely metals, polycyclic aromatic hydrocarbons, pharmaceuticals, and personal care products) of ecological changes across the study sites. The results showed inconsistencies between the WFD approach and the multivariate approach, as well as between the responses of macroinvertebrates and diatoms. The WWTP effluents impacted benthic communities in a single case: macroinvertebrates were negatively affected by one of the WWTP effluents, likely by the transported pharmaceuticals (other stressors are essentially homogeneous among sites). Given the findings and the scarcity of consistent evidence on ecological impacts that WWTP effluents may have in recipient ecosystems, further research is needed towards more sustainable regulation and linked environmental protection measures.

Significant improvement in freshwater invertebrate biodiversity in all types of English rivers over the past 30 years

There remains a persistent concern that freshwater biodiversity is in decline and being threatened by pollution. As the UK, and particularly England, is a densely populated nation with rivers of modest dilution capacity, this location is very suitable to examine how freshwater biodiversity has responded to human pressures over the past 30 years. A long-term dataset of 223,325 freshwater macroinvertebrate records from 1989 to 2018 for England was retrieved and examined. A sub-set of approximately 200 sites per English Region (1515 sites in total with 62,514 samples), with the longest and most consistent records were matched with predicted wastewater exposure, upstream land cover and terrain characteristics (latitude, altitude, slope gradient and flow discharge). To understand changes in macroinvertebrate diversity and sensitivity with respect to these parameters, the biotic indices of (i) overall family richness, (ii) Ephemeroptera, Plecoptera, Trichoptera (EPT) family richness, and (iii) the Biological Monitoring Working Party (BMWP) scores of NTAXA (number of scoring taxa) and (iv) ASPT (average score per taxon) were selected. A review of how close the BMWP scores come to those expected at minimally impacted reference sites was included. For all latitudes, altitudes, channel slope, river size, wastewater exposure levels, and differing proportions of upstream woodland, seminatural, arable and urban land cover, all diversity or sensitivity indices examined improved over this period, although this improvement has slowed in some cases post 2003. Mean overall family richness has increased from 15 to 25 family groups, a 66 % improvement. The improvement in mean EPT family richness (3 to 10 families, >300 % improvement), which are considered to be particularly sensitive to pollution, implies macroinvertebrate diversity has benefited from a national improvement in critical components of water quality.

Pesticide pollution associations with riverine invertebrate communities in England

Globally freshwater biodiversity has experienced major decline and chemical pollutants are believed to have played a significant role in this decline, but this has not been well quantified for most riverine invertebrate populations. Here we applied a biogeographically independent trait-based bioindicator, SPEARpesticides across sites across five regions (Northern, Midlands and Western, Anglian, Southeast, and Southwest) in England to investigate for associations specifically between pesticide use/pollution and riverine invertebrate communities over a 55-year period (1965-2019). Both spatially and temporally post-1990, the Anglian and Thames regions consistently showed the lowest SPEARpesticides scores, illustrating the presence of fewer pesticide sensitive species. The Anglian region had the highest pesticide use compared to all other regions from 1990 to 2018 and there were negative relationships between the level of pesticide/insecticide use and the regional SPEARpesticides score. Biochemical Oxygen Demand and ammonia, as measures of general water quality, were also negatively correlated with the SPEARpesticides scores across the regions, but these factors were not the driver for the lower SPEARpesticides scores seen in the Anglian region. Based on SPEARpesticides scores, riverine invertebrate communities in England have been most impacted in the Anglian region and we evidence chronic insecticide exposure is likely a significant factor in shaping the status of those invertebrate communities.

Flushing away the future: The effects of wastewater treatment plants on aquatic invertebrates

Wastewater treatment plants (WWTP) are essential infrastructure in our developing world. However, with the development and release of novel entities and without modern upgrades, they are ineffective at fully removing micropollutants before treated effluents are released back into aquatic environments. Thus, WWTPs may represent additional point source impacts to freshwater environments, further pressuring aquatic fauna and already vulnerable insect communities. Previous studies - mostly focusing on single WWTPs - have shown general trends of freshwater invertebrate communities becoming dominated by pollution tolerant taxa. To expand on these findings, the current study is the first to comprehensively investigate data on the effects of 170 WWTPs on invertebrate taxonomic composition. We compared data for several diversity and pollution indices, as well as the taxonomic composition both upstream and downstream of the WWTPs (366 sampling sites). In terms of abundance, the three most frequent and negatively impacted orders were the Plecoptera, Trichoptera and Gastropoda, while the Turbellaria, Hirudinea and Crustacea increased in abundance. Although strong changes in community composition were observed between upstream and downstream sites (mean species turnover of 61%), commonly used diversity indices were not sensitive to these changes, highlighting their potential inadequacy in accurately assessing ecological health. Our results indicate that WWTPs change downstream conditions in favour of pollution tolerant taxa to the detriment of sensitive taxa. Order-level taxonomic responses can be informative but should be interpreted with caution, since they can be driven by a few taxa, or opposing responses of species in the same group can result in an overall low order-level response. Upgrading WWTPs via additional treatment steps or merging may be beneficial, provided upstream sections are unimpacted and/or are in a good chemical and structural condition.

Two decades of the EU Water Framework Directive: Evidence of success and failure from a lowland arable catchment (River Wensum, UK)

The EU Water Framework Directive (WFD) is widely regarded as a seminal piece of environmental legislation. However, two decades since its inception, many European waterbodies are failing to meet its ambitious goal to ensure 'good' quantitative and qualitative status. Here, we investigate the impact of the WFD upon the environmentally sensitive yet heavily impacted River Wensum, a lowland arable catchment in eastern England. Compiling a dataset of 10,950 water quality samples collected from 57 sites across the catchment at approximately monthly intervals during 2000-2022, we assess the spatio-temporal dynamics of 12 priority pollutants, identify the major drivers of water quality change, and evaluate current and future compliance with WFD goals. Our analysis reveals improvements in wastewater treatment initiated significant declines (11-50 %) in the concentration of key sewage pollution indicators (phosphorus, ammonium, biological oxygen demand (BOD)) during the early 2000s. Conversely, agricultural pollution indicators (nitrogen, suspended solids, pesticides) displayed either limited change or a deterioration in water quality, with oxidised nitrogen concentrations in particular having increased 23 % during 2015-2022. Concentration spikes of organic chemical contaminants in recent years (propyzamide, tetrachloroethylene) raise concerns about increased riverine pollution from hazardous substances. Similarly, changes in winter (+13 %) and summer (-7 %) discharge over the past two decades have increased the risk of diffuse pollution mobilisation and reduced the dilution of point source pollutants, respectively. By 2022, 'good' or 'high' water quality status for organic matter pollution indicators (dissolved oxygen, BOD, ammonium) was achieved for >98 % of samples, however WFD compliance fell to just 46 % for phosphorus and 1.8 % for nitrogen. Projections to the end of the third River Basin Management Plan cycle (2027) reveal that whilst phosphorus compliance is likely to improve, nitrogen compliance failure will persist due to the existence of catchment legacy stores and climate change induced impacts on nitrogen mobilisation.

Tertiary wastewater treatment combined with high dilution rates fails to eliminate impacts on receiving stream invertebrate assemblages

The amount of wastewater processed in treatment plants is increasing following more strict environmental regulations. Treatment facilities are implementing upgrades to abate the concentrations of nutrients and contaminants and, thus, reduce their effects on receiving systems. Although many studies characterized the chemical composition and ecotoxicological effects of treated wastewater, its environmental effects are still poorly known, as receiving water bodies are often subjected to other stressors. We performed a field manipulative experiment to measure the response of invertebrate assemblages to one year of tertiary-treated wastewater discharges. We poured treated wastewater from an urban wastewater treatment plant into the lower-most 100-m of a previously unpolluted stream (3.6 % daily flow on average) while using another upstream reach as control. The positive correlation between effect sizes of abundance changes and IBMWP scores suggested assemblage modifications were following taxa tolerance to ecological impairment. The treatment increased the temporal variability of SPEARorganic, EPT relative abundance, and invertebrate functional redundancy. Our results show that even in this best-case scenario of tertiary-treated and highly diluted wastewater, the abundance of the most sensitive taxa in the aquatic assemblages is reduced. Further improvements in wastewater treatments seem necessary to ensure these effluents do not modify receiving water ecosystems.

Is water quality in British rivers "better than at any time since the end of the Industrial Revolution"?

We explore the oft-repeated claim that river water quality in Great Britain is "better now than at any time since the Industrial Revolution". We review available data and ancillary evidence for seven different categories of water pollutants: (i) biochemical oxygen demand (BOD) and ammonia; (ii) heavy metals; (iii) sewage-associated organic pollutants (including hormone-like substances, personal care product and pharmaceutical compounds); (iv) macronutrients (nitrogen and phosphorus); (v) pesticides; (vi) acid deposition and (vii) other variables, including natural organic matter and pathogenic micro-organisms. With a few exceptions, observed data are scarce before 1970. However, we can speculate about some of the major water quality pressures which have existed before that. Point-source pollutants are likely to have increased with population growth, increased connection rates to sewerage and industrialisation, although the increased provision of wastewater treatment during the 20th century will have mitigated this to some extent. From 1940 to the 1990s, pressures from nutrients and pesticides associated with agricultural intensification have increased in many areas. In parallel, there was an increase in synthetic organic compounds with a "down-the-drain" disposal pathway. The 1990s saw general reductions in mean concentrations of metals, BOD and ammonia (driven by the EU Urban Waste Water Treatment Directive), a levelling out of nitrate concentrations (driven by the EU Nitrate Directive), a decrease in phosphate loads from both point-and diffuse-sources and some recovery from catchment acidification. The current picture is mixed: water quality in many rivers downstream of urban centres has improved in sanitary terms but not with respect to emerging contaminants, while river quality in catchments with intensive agriculture is likely to remain worse now than before the 1960s. Water quality is still unacceptably poor in some water bodies. This is often a consequence of multiple stressors which need to be better-identified and prioritised to enable continued recovery.

Patterns of invertebrate functional diversity highlight the vulnerability of ecosystem services over a 45-year period

Declines in invertebrate biodiversity^1,2 pose a significant threat to key ecosystem services.^3-5 Current analyses of biodiversity often focus on taxonomic diversity (e.g., species richness),^6,7 which does not account for the functional role of a species. Functional diversity of species' morphological or behavioral traits is likely more relevant to ecosystem service delivery than taxonomic diversity, as functional diversity has been found to be a key driver of a number of ecosystem services including decomposition and pollination.^8-12 At present, we lack a good understanding of long-term and large-scale changes in functional diversity, which limits our capacity to determine the vulnerability of key ecosystem services with ongoing biodiversity change. Here we derive trends in functional diversity and taxonomic diversity over a 45-year period across Great Britain for species supporting freshwater aquatic functions, pollination, natural pest control, and agricultural pests (a disservice). Species supporting aquatic functions showed a synchronous collapse and recovery in functional and taxonomic diversity. In contrast, pollinators showed an increase in taxonomic diversity, but a decline and recovery in functional diversity. Pest control agents and pests showed greater stability in functional diversity over the assessment period. We also found that functional diversity could appear stable or show patterns of recovery, despite ongoing changes in the composition of traits among species. Our results suggest that invertebrate assemblages can show considerable variability in their functional structure over time at a national scale, which provides an important step in determining the long-term vulnerability of key ecosystem services with ongoing biodiversity change.

Impact assessment of a large panel of organic and inorganic micropollutants released by wastewater treatment plants at the scale of France

Micropollutants emitted by Human activities represent a potential threat to our health and aquatic environment. Thousands of active substances are used and go to WWTP through wastewaters. During water treatment, incomplete elimination occurs. Effluents released to the environment still contain part of the micropollutants present in the influents. Here, we studied the potential impacts on Human health and aquatic environment of the release of 261 organic micropollutants and 25 inorganic micropollutants at the scale of France. Data were gathered from national surveys, reports, papers and PhD works. The USEtox ® model was used to assess potential impacts. The impacts on Human health were estimated for 94 organic and 15 inorganic micropollutants and on aquatic environment for 88 organic and 19 inorganic micropollutants highlighting lack of concentration and toxicological data in literature. Some Polycyclic Aromatic Hydrocarbons and pesticides as well as As and Zn showed highest potential impacts on Human health. Some pesticides, PCB 101, βE2, Al, Fe and Cu showed highest potential impacts on aquatic environment.

Learning from the past and considering the future of chemicals in the environment

Knowledge of the hazards and associated risks from chemicals discharged to the environment has grown considerably over the past 40 years. This improving awareness stems from advances in our ability to measure chemicals at low environmental concentrations, recognition of a range of effects on organisms, and a worldwide growth in expertise. Environmental scientists and companies have learned from the experiences of the past; in theory, the next generation of chemicals will cause less acute toxicity and be less environmentally persistent and bioaccumulative. However, researchers still struggle to establish whether the nonlethal effects associated with some modern chemicals and substances will have serious consequences for wildlife. Obtaining the resources to address issues associated with chemicals in the environment remains a challenge.