Interactions with freshwater biofilms cause rapid removal of common herbicides through degradation - evidence from microcosm studies

We investigated the role of periphyton biofilms for the fate of three common herbicides, i.e. bentazone, metazachlor and metribuzin, at low, environmental levels and 100 times higher, during a 16 days laboratory experiment. We found that herbicide water concentrations were stable during the first 8 days, whereas substantial declines (>78%) occurred between days 8-16 for all three herbicides. These rapid declines were explained only to a small extent (<8% of the total herbicide loss) by biofilm sorption. As herbicide concentrations in light and dark treatments without biofilms were similar, and the applied light regimen did not cover the UV-spectrum, herbicide photolysis was ruled out as a possible explanation for the observed declines. Furthermore, based on the compounds' characteristics, also volatilization was judged negligible. Therefore, we conjecture that the observed declines in herbicides were due to biodegradation and subsequent evasion of (CO2)-C-14 that was driven by enzymatic action from heterotrophic microbes. We reason that heterotrophic microbes used herbicide molecules as labile organic C-sources during C-limitation. Future studies should identify the microbial communities and genes involved in biodegradation in order to understand better the role of biofilms for the self-purification of surface waters

Zebra mussels (Dreissena polymorpha) for assessing microbial contamination and antibiotic resistant bacteria in freshwaters

The suitability of zebra mussels (Dreissena polymorpha) as biomonitoring organisms for faecal contamination of surface waters was examined in both laboratory and field experiments. In addition, the presence of antibiotic resistant bacteria was investigated. In the first two laboratory experiments, the mussels were first exposed to a known concentration of Escherichia coli and Enterococcus facecalis and then depurated. In the other two experiments, the mussels were exposed to a tenfold dilution of sewage treatment plant effluent and then depurated. Zebra mussels showed a maximum uptake and elimination rate during the first hours after exposure to contaminated, and respectively, clean water. The field experiment was conducted at 6 sites located upstream and downstream from the sewage treatment plant outlet in the Fyris river (Uppsala, Sweden). During the 19 days of exposing caged mussels, the presence of faecal indicators, as well as Salmonella spp. was investigated. All the experiments demonstrated the ability of the zebra mussels to accumulate much higher concentrations of bacteria than in the surrounding water. This is in accordance with the work of previous studies and sustains the usefulness of zebra mussels in detecting bacterial peaks. Salmonella spp. was found on three occasions at the outlet, in both mussels and water, and on two occasions in the water downstream. All the E. coli and 41.3 % of the Enterococcus spp. isolates from both water and mussels were resistant to at least one antibiotic. A large percentage (48.5 %) of those found in mussels was multi drug resistant, thus providing evidence for this emerging problem that needs to be controlled

Use and environmental impact of antifouling paints in the Baltic Sea

Biocide-based antifouling (AF) paints are the most common method for preventing biofouling, i.e. the growth of algae, barnacles and other organisms on boat hulls. AF paints for leisure boats are predominantly based on copper (Cu) as the main biocide, with zinc (Zn) present as a pigment and stabilizer. Both metals are released from the paint matrix into the water column, leading to contamination of marinas which typically have only limited water exchange. Thus, the aim of this PhD thesis was to describe the use of AF paints in different regions in Sweden, as well as the associated environmental consequences with regard to contamination of the environment and toxicity to non-target aquatic snails. Using a recently developed X-ray fluorescence application, high levels of Cu were detected on boats moored in freshwaters, despite a more than 20-year-old ban, as well as high levels of tin (Sn) on 10 % of the boats, indicating the presence of (old) tributyltin paints (TBT), which might pose an environmental risk and a health hazard for people performing the paint scraping (paper 1). In addition, very high levels of Cu and Zn were measured in the biofouling material collected from the boat hulls, and this is problematic because the biofouling is commonly disposed of on the soil in boatyards at the end of each season. No difference was found in the amount of biofouling on boats coated with Cu or biocide-free paints, which implies that Cu might be currently overused in areas of low salinity and low barnacle density (paper 2). This work also introduces the use of a new species for ecotoxicological field experiments, the snail Theodoxus fluviatilis. Chronic field experiments (paper 3) revealed 6-fold increases in snail mortality, negative growth and up to 67-fold decreased reproduction in marinas, compared to areas not impacted by boating (‘reference areas’). Moreover, a higher prevalence of snails with histopathological alterations (e.g. necrosis of gills, gonads, midgut gland and parasite infestation, among others) was observed in the marinas, compared to the reference areas (paper 4). Statistical modelling indicated that the majority of the toxic effects were best predicted by the metals, most likely originating from AF paints. The results presented in this thesis depict some important aspects of AF paint use in brackish water and highlight the necessity of implementing a suitable management practice for the heavily contaminated biofouling waste in order to minimize the risk to soils. In addition, the evidence of toxicity to snails in marinas can be used as a basis to increase the public understanding of the impact of recreational boating and encourage people to choose less toxic alternatives to AF paints.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p

Pesticide Mixtures Cause Short-Term, Reversible Effects on the Function of Autotrophic Periphyton Assemblages

In a laboratory experiment we investigated the effects of pesticide mixtures on the structure and function of freshwater biofilms, with focus on their photoautotrophic component. We identified 6 herbicides and 1 fungicide commonly found in Swedish streams at relatively high concentrations and created 3 ternary mixtures that were tested in concentration series ranging from observed environmental concentrations to up to 100 times higher. Biofilms were exposed to these pesticide mixtures for 8 d and then allowed to recover for another 12 d. Our results show a rapid and consistent inhibition of photosynthesis after just 24-h exposure to the highest test concentration of pesticides, as well as in some treatments with lower concentrations (i.e., 10 times the environmental level), on exposure. Interestingly, the observed effects were reversible because biofilm photosynthesis recovered rapidly and completely in clean media in all but one treatment. In contrast to the functional response, no effects were observed on the algal assemblage structure, as assessed by diagnostic pigments. We conclude that the pesticide mixtures induce a rapid but reversible inhibition of photosynthesis, without short-term effects on biofilm structure. Environ Toxicol Chem 2020;00:1-8. (c) 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC

New analytical application for metal determination in antifouling paints

Despite the ban of applying TBT coatings on leisure boats in the late 80s, recent studies show an ongoing spread of TBT from leisure boats, particularly during hull cleaning events. Therefore, countries in EU have adopted expensive measures to clean this wash water. A more cost-efficient measure is to focus directly on the source, i.e. identify leisure boats with high concentrations of TBT and prescribe boat owners to remove the paint. We have developed a new antifouling paint application for a handheld X-ray fluorescence (XRF) analyzer to be used for identifying boats with high area concentrations (μg/cm²) of Sn (indication that the hull contains TBT paint residues). Copper and zinc are also included in the application since these metals are used in the vast majority of today's paints. A blind test with up to four layers of TBT-, copper- and zinc-based paints showed good correlation between XRF-measured area concentrations and chemically analyzed concentrations. Future usage of the applications involves identification of boat hulls in particular with high Sn concentrations and also with high Cu and Zn concentrations. This method has the potential to become a useful tool in regulatory management of existence and use of toxic elements on boat hulls

XRF measurements of tin, copper and zinc in antifouling paints coated on leisure boats

Tributyltin (TBT) and other organotin compounds have been restricted for use on leisure boats since 1989 in the EU. Nonetheless, release of TBT is observed from leisure boats during hull maintenance work, such as pressure hosing. In this work, we used a handheld X-ray Fluorescence analyser (XRF) calibrated for antifouling paint matrixes to measure tin, copper and zinc in antifouling paints coated on leisure boats in Sweden. Our results show that over 10% of the leisure boats (n = 686) contain >400 μg/cm2 of tin in their antifouling coatings. For comparison, one layer (40 μm dry film) of a TBT-paint equals ≈ 800 μg Sn/cm2. To our knowledge, tin has never been used in other forms than organotin (OT) in antifouling paints. Thus, even though the XRF analysis does not provide any information on the speciation of tin, the high concentrations indicate that these leisure boats still have OT coatings present on their hull. On several leisure boats we performed additional XRF measurements by progressively scraping off the top coatings and analysing each underlying layer. The XRF data show that when tin is detected, it is most likely present in coatings close to the hull with several layers of other coatings on top. Thus, leaching of OT compounds from the hull into the water is presumed to be negligible. The risk for environmental impacts arises during maintenance work such as scraping, blasting and high pressure hosing activities. The data also show that many boat owners apply excessive paint layers when following paint manufacturers recommendations. Moreover, high loads of copper were detected even on boats sailing in freshwater, despite the more than 20 year old ban, which poses an environmental risk that has not been addressed until now

Limited effects of pesticides on stream macroinvertebrates, biofilm nematodes, and algae in intensive agricultural landscapes in Sweden.

Bighiu MA, Höss S, Traunspurger W, Kahlert M, Goedkoop W. Limited effects of pesticides on stream macroinvertebrates, biofilm nematodes, and algae in intensive agricultural landscapes in Sweden. Water research. 2020;174: 115640.Pesticides are frequently detected in surface waters, sometimes at levels exceeding ecotoxicological guidelines. We screened for almost 100 pesticides in 32 streams from intense agricultural areas in Southern Sweden, in concert with water chemistry parameters. In addition, we investigated the communities of benthic macroinvertebrates, biofilm nematodes and algae and calculated multiple bioassessment metrics. The number of pesticides found in each stream ranged between 2 and 52, but the sum of Toxic Units (SigmaTU) for the mixtures was generally low, and exceeded the European Uniform Principles only in a single sample for algae and in 2% of the samples for Daphnia. Only nematode communities were significantly correlated with the SigmaTU, potentially due to their higher pesticide exposure in biofilms. Diatom metrics showed that most streams were impacted by eutrophication and macroinvertebrate metrics showed good status in most streams, whereas the SPEARpesticides (SPEcies At Risk) index, specifically designed to indicate pesticide effects, showed that about half of the samples were at risk. Interestingly, SPEARpesticides was not correlated to SigmaTUDaphnia, and this discrepancy suggests that redefining the boundaries for quality classes might be necessary for this index. Moreover, SPEARpesticides was positively correlated with the commonly used macroinvertebrate index ASPT, although disparate results were found for several streams. We argue that this questions the scaling of both metrics and the specificity of their responses. We discuss that the overall good/moderate status of the streams, despite the intense agriculture in the catchments, can be due to the fact that i) a sampling strategy with repeated grab samples did not capture peak pesticide concentrations, thus underestimating acute exposure, ii) pesticide run-off indeed was low, due to measures such as buffer strips, and iii) the nutrient-rich conditions and high sediment loads counteracted pesticide toxicity. We conclude that agricultural land use was the overriding stressor in the investigated streams, including strong effects of nutrients, less apparent effects of pesticides and likely impact of hydromorphological alterations (not specifically addressed in this study). Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved

Metal contamination in harbours impacts life-history traits and metallothionein levels in snails

<div><p>Harbours with limited water exchange are hotspots of contaminant accumulation. Antifouling paints (AF) contribute to this accumulation by leaching biocides that may affect non-target species. In several leisure boat harbours and reference areas in the Baltic Sea, chronic exposure effects were evaluated using caging experiments with the snail <i>Theodoxus fluviatilis</i>. We analysed variations in ecologically relevant endpoints (mortality, growth and reproduction) in concert with variation in metallothionein-like proteins (MTLP) levels. The latter is a biomarker of exposure to metals, such as copper (Cu) and zinc (Zn), which are used in AF paints as active ingredient and stabilizer, respectively. In addition, environmental samples (water, sediment) were analysed for metal (Cu and Zn) and nutrient (total phosphorous and nitrogen) concentrations. All life-history endpoints were negatively affected by the exposure, with higher mortality, reduced growth and lower fecundity in the harbours compared to the reference sites. Metal concentrations were the key explanatory variables for all observed adverse effects, suggesting that metal-driven toxicity, which is likely to stem from AF paints, is a source of anthropogenic stress for biota in the harbours.</p></div