“Wastewater effluents should be considered potentially harmful mixtures”


Baltic Breakfast: Micropollutants in wastewater – a problem of unknown magnitude

Micropollutants is a term for a wide range of chemicals present in water bodies as a result of human activities. Urban wastewater treatment plants function as collection points for these pollutants, and in the Chempact project researchers from several countries around the Baltic Sea have studied how the effluents from these plants are analyzed and what chemicals they contain. The results from the project, and related research, were presented at a recent Baltic Breakfast.

Text and photo: Lisa Bergqvist

In today’s society, chemicals are released from a wide range of human activities, to later be found in surface waters through different pathways. Wastewater treatment plants function as collection points, where many pollutants are collected in effluents and sludge. However, it’s unclear how important this pathway is, compared to others, such as atmospheric deposition.

 –  This is of interest for managers, as there are possibilities to treat wastewater better and there is also an opportunity here to monitor what kind chemicals we are emitting in our societies, explains Emma Undeman, researcher at Stockholm University Baltic Sea Centre.

Emma Undeman and her colleagues in the Chempact project have tried to contribute to one piece of this complex puzzle, by compiling data on concentrations of organic contaminants and metals that have been measured in effluents in the Baltic Sea catchment. The study contains data from 725 wastewater treatment plants and shows large differences between countries regarding what analysis, if any, are performed at the plants. 

In total, around 1100 substances have been analyzed. Most common is to analyze industrial chemicals and pharmaceuticals, whilst ingredients in household and personal care products are often overlooked. 

 – Sweden has analyzed a broader range of substances. This is partly because Sweden quite often has screening campaigns in the national monitoring program looking for chemicals of emerging concerns, says Emma Undeman.

Moderator Marie Löf, Stockholm University Baltic Sea Centre.

So, what is found in the wastewater? 

 – There are huge amounts of chemicals used as complexing agents, water softeners used in detergents. Also, metals are often present in high concentrations, for example zinc.

Organophosphate esters, solvents, synthetic musk, sunscreens, fluorescent whitening agents, process chemicals from plastic production and pharmaceuticals are others on the concentration top list.

 – It’s a heterogenous dataset and it’s hard to make comparisons and load estimations. We would like to see more countries analyze a wider range of substances, to get a better idea of what is actually present in the wastewater, says Emma Undeman.

Emma Undeman, Stockholm University Baltic Sea Centre.

Large differences between groups of micropollutants

Ksenia Pazdro, Head of Marine Chemistry and Biochemistry Department, and her colleagues at the Polish Academy of Science, has long experience of studying micropollutants in Polish marine waters. In the Gulf of Gdansk, an area strongly impacted by multiple stressors such as cities, shipping and tourism, around 100 different micropollutants have been measured.

However, there are large differences between groups of pollutants when it comes to data availability and establishments of threshold safe limits.

 – For legacy pollutants, like regulated heavy metals and persistent organic pollutants, data availability is good. The threshold safe limits are well established and we can establish long-term trends because we have long time series, says Ksenia Pazdro.

One example is brominated flame retardants, used in several products. For this group of chemicals, the sources are well identified and also partly eliminated, since the use has been banned. The concentrations in blue mussels and flounder have decreased the last two decades, but the safe levels for fish are still exceeded.

Ksenia Pazdro, Polish Academy of Science.

The situation is completely different with new emerging micropollutants, such as bisphenol A, used in several synthetic materials and found in many products, and pharmaceutical residues. Here the data sets are very scarce and there are often no safe levels established, but for example the pain killer diclofenac and some antibiotics like sulfamethoxazole and oxytetracycline have been assessed to pose high or medium risks for non-target organisms. 

 – It’s obvious that some local wastewater treatment plants are important sources because pollutants were found in effluents and also in Vistula river, that is collecting water from a large area with several plants.

Current knowledge shows that for many micropollutants in the coastal zone, dilution seems not to be a solution, says Ksenia Pazdro.

 – Some regulatory actions should be proposed, like admissible levels in effluents and improvements in wastewater treatment technology. But we cannot neglect the personal actions. One thing we can do ourselves is to return unused medicines to the pharmacy, instead of throwing them in the toilet. 

Matti Leppänen, Finnish Environment Institute.

Effects on biota have been seen

Matti Leppänen, Adjunct professor in ecotoxicology at Finnish Environment Institute (SYKE), explains that the shallow coastal zones in the Baltic Sea act like buffer zones for the open water, and are also exposed to local sources of contamination. The ecosystem in the Baltic Sea could be particularly vulnerable to contamination as it contains a mixture of marine and freshwater species that might have low tolerance to disturbances. 

In the global literature wastewater effluents have shown to have several effects on biota. The most notorious is endocrine disruptors having hormonal effects on organisms living downstream the plants, resulting in feminization of fish and mussels. 

 – Also, many kinds of biomarkers of stress are induced in mussels and fishes. Population level effects have also been recorded as a decrease in number of species or change in species structure, says Matti Leppänen.

Some of these effects have also been seen in the few studies available from the Baltic Sea. Mussels caging at the pipe ends have for example shown to suffer from oxidative stress (Finland), increased heart rate (Estonia) and be genetically different than others (Sweden).

 – What we should do with effluents to protect the environment is to consider them as potentially harmful mixtures, says Matti Leppänen.

For more accurate estimates of the combined effects and risks of these micropollutants he suggests summing up the risks of the single harmful chemicals that are found and to use biotests to study the effects in living animals.

 – We should also consider upgrading the treatment plants, using for example active carbon or different membranes. That will cost something, or maybe a lot. But maybe we should follow the rule polluter pays, he says.


Answers to the questions from the audience

With 350,000 registered chemicals, the problem of management/measurement and regulation seems insurmountable! What kinds of approach could possibly stand a chance of protecting our health and the health of the ecosystems? 

Emma: It is a challenge to use chemicals in a way that doesn’t harm the environment or human health. We need to find better methods to identify the substances that have to be substituted, preferably before putting them on the market, and also consider mixture effects in the risk assessments as well as recognizing the risk of unpredictable effects. We discuss this issue eg in this paper: https://www.scielo.br/pdf/alb/v31/2179-975X-alb-31-e106.pdf

Ksenia: Another idea to reduce emissions is replacement of harmful substances by less harmful ones, (e.g. replacement of traditional solvents by ionic liquids). Concerning active substances in pharmaceutical formulations it seems to be more complicated, we cannot replace them, but often we can use e.g. over-the-counter pharmaceuticals in a more reasonable way, moreover improvement in WWTP  technologies may reduce their emissions (on the other hand these action may be expensive) to recipients.

Matti: Chasing single chemicals from environment (water, air, soil, inhouse etc.) seems to be too demanding task unless there is a clear idea what is possibly causing a problem. I see only success in preventing emissions and finding sources. Environmental permits are one tool, education another. Analyzing emissions and environmental matrices should also use tools that measure mixtures; non target analysis in chemistry and effect-based methods (biotests) followed by effect-directed analysis (chemistry).

How could the cell line based biotests Matti mentioned be used in e.g. recipient control programs?

Matti: There are several receptor-based cell line tests available that indicate specific toxic response. Those respond to all molecules able to bind to that specific receptor. For example, with estrogenic substances mixture response measured on y-axis is compared to reference compound (estradiol, E2) response. This gives equivalent concentration in E2 (e.g. ng/L E2) for that particular sample. As there already is an established threshold value for the safe E2 concentration set for aquatic life, this threshold value could be used as a limit that cannot be exceeded.

How can we minimize the amount of the micropollutants in the wastwater? 

Emma: We need to work both with reducing emissions at source and use opportunities to use broad precautionary measures that help reducing the load of both known and unknown substances, we discuss this in a previous policy brief.

Matti: Limit pollutant emissions in its source (influent) and/or improving the purification methods in the treatment plants.

How can we “restore” the sea from the micropollutants?

Emma: We need to ensure that we reduce emissions of hazardous substances so they don’t enter in the first place. Many persistent substances (eg PCBs, PBDEs, PFASs) have already been released to the environment and are stored in sediments and in the water column, they will eventually degrade and dissipate but it will take a long time. Many micropollutants that are present in elevated levels in rivers and coastal zones are not particularly persistent, and will quickly disappear if the emissions stop. 

Ksenia: Theoretically contaminants especially those being hydrophobic are accumulated efficiently in sediments .

Matti: Only time is working for us. Theoretically, if a substance bioaccumulates efficiently, removing contaminated fish could do the job but is hardly working in large targets like sea. There is a publication calculating how fish removal could help in dioxin problem of the Baltic Sea.

What chemicals found in wastewater do you find most worrying?

Emma: It is difficult to judge which substances that have the largest negative impact on the environment, but for example the presence of many PFASs in effluents is worrisome as these are in general mobile and extremely persistent substances that will not disappear quickly even if we stop production and use, in case we would discover an urgent need to do so (as has already been discovered for several PFASs). These substances may enter the aquatic environment via many different pathways, but presence in wastewater indicates a widespread use/emissions in urban settings. 

Ksenia: Persistent/bioaccumulative/mobile. I agree that PFAS group is a very good example.

Matti: Those that are persistent, bioaccumulate and are toxic. Also, a combination of persistence, mobile and toxic is worrying. PFAS group is infamous one.

What are the proportion of the effect from unknown substances to the total effect?

Emma: This is very difficult to judge. On the one hand, it is often found that a limited number of substances contribute the main fraction of total toxicity of a chemical mixture. However, this is also dependent on the target organism. The known substances in a chemical mixture (such as wastewater) may explain the majority of toxic effect with respect to one end point (eg herbicides explain effect on algea) but not another (eg fish). See for example this article discussing this issue: https://www.sciencedirect.com/science/article/pii/S004313541300170X  

Matti: If you mean effect in biota, it depends what is the effect. For example, in effluents female hormones (natural and medical) can explain only few percent to 70% of total estrogenic activity in a sample and it varies with the WWTP. 

Emma, will the database be publicly available?

Emma: We will submit a scientific article this spring, the database will then be available.

Did any of the speakers also investigate or has experienced the potential pathway for micropollutants of wastewater from ships?

Emma: I don’t do research in this area myself, however projects on this topic are ongoing, for example: www.chalmers.se/sv/projekt/Sidor/EvaluationQ-control-and-Mitigation-of-the-EnviRonmental-impacts.aspx

Ksenia: MARPOL convention and HELCOM Technical Guidance for the Handling of Wastewater in Ports of the Baltic Sea (2019)could be an interesting source of information (of course it is a more general information not devoted to micropollutants, see also article in Sustainability, 2020, A. Martínez-López et al. and related references.

Matti: No, I have not, it could be a relevant source at least to do an initial assessment.

Matti, what were the test organisms in the Baltic WWTP toxicity data (i.e. heart rate)?

Matti: The mussel Macoma balthica.

Would you consider relevant to also consider microplastics in WWTPs effluents?

Emma: I don’t know. 

Ksenia: In my opinion WWTPs are not the most important source of microplastics, in fact microplastics are everywhere around us so other sources – deposition from atmosphere, rivers seem to be more important for coastal zones than WWTPs.

Matti: Microplastics can carry micropollutants, either by ad/absorbing them and those also contain additives that can be pollutants and be released in aquatic environment. However, most plastic particles end up to the sludge.

Emma, a small correction - Ukraine does not have any water flows to the Baltic Sea, so it is not relevant for project.

Emma: A small part of the Baltic Sea catchment is located in Ukraine (although far away from the sea) and some other non-HELCOM countries, see eg the PLC-6 report from HELCOM: helcom.fi/wp-content/uploads/2020/01/PLC-6-background-report.pdf

Why are effect-based methods not used to a greater extent in the wastewater treatment plants? 

Matti: Usually something extra work is not done unless there is a clear motivation, and I believe it is mainly missing. Also, threre should be generally accepted thresholds or limit values for interpretation of the biotest results. It is difficult to act without or see the significance. 

What different types of effect-based methods would you recommend in wastewater treatment plants as a complement to analysing single chemicals?

Matti: A battery of test containing both in vitro (e.g. receptor based cell line tests) and in vivo (living animals) tests. The former are handy for detecting specific effects that helps in search of possible drivers of toxicity. The latter show the cocktail effects in whole animal and includes accumulation, metabolism and elimination reactions. In vivos can also connect to chronic, population level endpoints (growth, reproduction). Standard ISO/OECD tests with algae, invertebrates and fish embryos would be a could starting point to discuss.

You mentioned that one common approach in this context is ’dilution is the solution’, how big a problem is micropollutants from wastewater treatment plants for organisms in the Baltic far away from the WWTPs? Is the long water exchange time of about 30 years in the Baltic a problem in this context? 

Matti: Chemical wise: Open sea organisms probably see only persistent chemicals, and of those able to accumulate/magnify. Ecology: Many open sea species are connected to coastal ecosystems either directly or via other species. Loss of biodiversity or contaminated pray can carry the effects farther. Long water change definitely does not help but I am not sure how significant factor it is. On the other hand, it also may reduce the transport btween the Baltic Sea basins. Transport modellers could estimate this phenomenon better.   

In a revision of the Urban Wastewater Treatment Directive, what would you like to tell officials, your national politicians and decision-makers at EU level as the most important thing when it comes to micropollutants?

Matti: Here I would advertise NORMAN network and Water Europe position paper that collects the present understanding and tools/initiatives how the latest advancements in science could improve protecting waters from effluents: www.normandata.eu/sites/default/files/files/Publications/Position paper_CECs UWW_NORMAN_WE_2019_Final_20190910_public.pdf

Start discussion on Emission Limit Values, nominate performance indicator substances and select a battery of biotests with thresholds for a routine monitoring of effluents. Build up an action plan when thresholds and limit values are exceeded.

We have talked about the Urban Wastewater Treatment Directive, but do you see the need to improve other EU legislation as well to protect our seas and lakes from micropollutants that are emitted from wastewater treatment plants?

Matti: Yes. WFD and maybe MSFD. There is a lot of discussion on the EBMs in the Working Group Chemicals (Commission run WG) and it is possible that in the future Watch list (as first step) will include estrogenicity EBM along the single chemicals. One of the main sources are UWWTPs.

Ksenia, how much and in what way could the concentrations of micropollutants affect biota in the Gulf of Gdansk? 

Ksenia: It is difficult to answer this question briefly, it depends on compound (e.g. many energing micropollutants show endocrine disrupting activities), some are/might be mutagenic/carcinogenic, the other may influence photosynthetic systems in algae. A lot depends also on the potential of bioaccumulation. Obvious that the effects of hazardous substances can be observed at all trophic (from algae to fish) and biological levels (biochemical, molecular, physiological etc) selected biological effects has been also introduced to national monitoring programme (micronucleus tests since 2014), however the test is not carried out systematically for the Gulf of Gdańsk area. There is one paper of Larsson et al. (2018) who carried out research in various Baltic Sea areas to assess the impact of selected point pollution sources on resident populations of the blue mussel (Mytilus edulis trossulus) using multiple biomarker approach. In the Gulf of Gdańsk no genotoxic or histological effects of sewage effluents on sampled blue mussels, neither elevated negative effect of endocrine disrupting compounds were observed close to point sources like sewage effluents. Some histopathological alterations were observed in gonads of collected mussels, however these changes occurred in M. edulis from the whole area of the Gulf with similar frequency. 

As I have mentioned in the presentation the concentrations of polybrominated flame retardants (persistent, bioaccumulative, toxic compounds) in the Gulf of Gdańsk (but also in other areas – see HELCOM BSEP 155, 2018) exceed thresholds (for some fish like herring and flounder). PBDEs have negative effects like immunosuppresion, oxidative stress, thyroid hormone transport etc.

In the case of several new emerging pollutants the situation is more complicated, thresholds are established only for few compounds, for other like pharmaceutical residues we assesss the risk based on so called RQ risk quotient calculated as the ratio measured concentration predicted no effect concentration (PNEC). To calculate PNEC toxicity benchmark corresponding to the lowest available ecotoxicity data for aquatic organisms such as short-time toxicity data (EC50), lowest observed effect concentration (LOEC) or no observed effect concentration (NOEC) and appropriate assessment factors are used. Unfortunately there is still a lack of ecotoxicity data from tests with marine species. Nevertheless, such calculations help to assess if the measured concentrations may affect biota, and one of the examples that was presented during the breakfast was sulfamethoxazole (antibacterial agent) concentrations in sediment at some sites may affect biota.

Diclofenac, a pain killer, is a specific example. It is one of the few pharmaceuticals with established environmental quality standard (EQS) values, as this compound was included in the EU first watch list. Several EQS:s have been proposed in Europe, ranging from 10 ng L−1 to 100 ng L−1. However, in July 2018, the European Commission adopted and published an updated Watch List (WL) of substances to be monitored in EU surface waters. In the case of diclofenac JRC recommendations were to remove it from the WL, and consequently, the second WL does not include this compound. Nevetheless, Helcom (2018) proposed a threshold of 5 ng L−1. This more restrictive threshold was proposed due to the fact that the distribution, role and fate of dioclofenac in the Baltic Sea are not clearly understood, with limited information from few monitoring and screening studies available. In case of Gulf of Gdansk waters this threshold was exceeded in case of many samples. 

Summarizing: more knowledge is needed and even if today we assume that no severe effects on biota are observed, nevertheless long term chronic effects of even low but constant concentrations should be assessed for single compounds but special focus should be given on mixture effects and also we should know which organisms will be most sensitive as we can’t forget that this ecosystem is characterzized by low biodiversity.

Do you see gradients from land to sea when studying concentrations of micropollutants in sediment in the Gulf of Gdansk? Can proximity to wastewater treatment plants or urban environment in general explain such gradients and is it possible to separate these? 

Ksenia: In fact in depends on which compounds we talk about. For hydrophobic organic compounds and metals, even close to the sources (e.g. Vistula mouth or WWTPs outlets) areas are often not rich in hydrophobic contaminants or metals as they are dominated by sandy sediments with low organic matter content (on the other hand these are very dynamic sites so occasionally we may observe high concentrations). The usual areas of accumulation (high levels of contaminants) are deeper parts of the Gulf with muddy sediments which are rich in organic matter. The most important area of accumulation is Gdańsk Deep. However, more hydrophilic compounds like several pharmaceutical residues ”escape” this pattern. These compounds have been detected in the Gdansk Deep sediments. However, the concentration are at similar or lower level than those from the vicinity of Vistula or WWTPs. No correlation was observed between their concentrations and organic matter content or other sediment features. It should also be underlined that the database is too poor and to draw more concrete conclusions we need more sampling (for these new emerging compounds).

Second question in case of Gdansk WWTP it is difficult to observe such gradient because the outlet is located quite close to Vistula mouth so it is difficult to separate the influence from both sources. Gdtnia Debogorze discharges also to the area influenced by many factors but there is is quite possible that we will be able to observe such gradient. The studies are planned for the nearest future.  

Ksenia, how did you choose which micropollutants to analyze for? 

Ksenia: First: good (means reliable) analytical methods etablished/developed and analytical equipment available. Compounds presence in freshwater ecosystems or soils in the vicinity of the study area: literature study based on the ecological importance of target compounds; possible toxic effects; presence in other costal ecosystems.

Production volume or consumption rate (like in case of pharmaceutical residues - Poland was placed among the countries with the highest levels of pharmaceutical consumption per capita in Europe)

Are WWTPs perceived as an important source in Poland that need to be managed better?

Ksenia: I think this becomes true mainly (mainly thanks to the projects implemented in this topic like Morpheus, Cohiba, NonHazCity etc) but only for the limited group of people. Examples: concentrations in effluents are not monitored for micropollutants even if stakeholders know that it should be done, but without regulatory actions nobody will invest (it seems to be quite expensive), similarly for effect-based monitoring and of course improvement of WWT technologies is on the top of the most expensive actions (so the answer ”is it worth to invest in it” should be very well justified from different perspectives).

See a recording of the webinar below