Understanding pollutant pathways to receiving water bodies is essential for implementing effective mitigation measures (including adequate treatment and/or source control) and meeting regulatory guidelines. The research for this Licentiate thesis aimed to improve knowledge of urban stormwater contributions to receiving water bodies, with a focus on common contaminants in stormwater runoff, and assess the potential risks these substances pose. The study is based on an extensive dataset collected from field sampling campaigns carried out along three urban streams in Sweden, all of which primarily receive untreated stormwater discharges through separate sewer systems when passing through urban areas.

Field sampling results indicate that during wet weather events, the concentrations of total suspended solids (TSS) and metals associated with anthropogenic activities originating from traffic-related activities and building and infrastructure materials – such as chromium (Cr), nickel (Ni), and zinc (Zn) – increase in the streams, confirming the impact of urban stormwater discharges. Further, the concentrations of per- and polyfluoroalkyl substances (PFAS) were also increased in the streams under wet weather conditions, with total quantified concentrations (sum of 34 PFAS) ranging from below the reporting limit up to 84.7 ng/L during dry weather and increasing under wet weather conditions (0.87 to 102.3 ng/L). The stormwater discharges introduced a great variety of PFAS to the streams, particularly longer chain PFAS. In sediments, both higher concentrations and a greater variety of PFAS were found at sampling sites located downstream of urban areas as well as sites close by known point sources, such as airports. Of all contaminant groups analyzed, PFAS stood out as the only compound family consistently detected in both the water and sediment phases. Most other organic contaminants, including phthalates and polycyclic aromatic hydrocarbons (PAHs), were not detected above reporting limits in stream water but were quantified in bottom sediments. The concentration and occurrence of these hydrophobic organic contaminants in bottom sediment followed the urbanization gradient, with higher concentrations observed at downstream sampling sites near urban areas or known point sources, such as industrial areas and airports, compared to upstream sites. This suggests that urban runoff mobilizes and transports these contaminants from urban areas to receiving water bodies, leading to their accumulation in sediments. In contrast, organotin compounds likely originate from sources other than stormwater runoff (remains unidentified), while phenolic substances did not exhibit a clear pattern indicative of transport through urban runoff.

Risk assessment of the streams revealed contamination levels in bottom sediments, where 20 out of 82 assessed compounds – including PAHs, phenols, phthalates, and PFAS – exceeded toxicity-based limits (i.e. Predicted No-Effect Concentration (PNEC) and Annual Average Environmental Quality Standards (AA-EQS)). In the sediment phase, exceedance rates ranged from 2 to 105 times. Notably, 4-tert-octylphenol (4-t-OP) exceeded PNEC by up to 105 times, while perfluorooctane sulfonate (PFOS) consistently surpassed the critical threshold, with concentrations reaching 140 times the toxicity-based threshold (PNEC). In the water phase, in general exceedance rates were lower than in bottom sediment, nevertheless exceedance rates for PFOS and Total PFOA Eqv remained critically high, particularly under wet weather conditions. Findings also highlighted the limitations of current risk assessment methods, which may underestimate risks primarily due to the lack of experimentally derived PNEC values.

Denna studie undersökte ekologiska effekter av urbanisering och urban dagvattenavrinning på vattendrag som passerar genom urbana områden. Diversitet av makroevertebrater (ryggradslösa djur) analyserades med environmental DNA (eDNA) metabarkodning av biofilmprover. Dessa har samlats in vid flera platser längs tre vattendrag i södra Sverige. Proverna samlades in längs en gradient från landsbygd uppströms till urbanpåverkade områden nedströms. Generellt dominerades makroevertebratsamhällena av föroreningståliga taxa, särskilt Chironomidae (fjädermyggor), vilket indikerar antropogent tryck längs provsträckan från uppströms till nedströms. Även om diversiteten ökade nedströms speglade detta en ökad heterogenitet av habitat som gynnar föroreningståliga arter snarare än ekologiska förbättringar, vilket speglar en möjlig påverkan från urbana områden och därmed från dagvatten.

Dagvattenutsläpp kan ge upphov till biologiska effekter i urbana vattenmiljöer. I denna studie togs bottensedimentprover från fyra vattendrag, både uppströms och nedströms urbana och industriella områden. Proverna analyserades med fem in vitro-biotester som riktar in sig på aktivering av östrogenreceptorer (ER), androgenreceptorer (AR), arylkolvätereceptorer (AhR), hämning av AR (Anti-AR) samt induktion av oxidativ stress (Nrf2). Resultaten kompletterades med kemisk analys av 82 föroreningar som förekommer i urban avrinning. Så kallad "iceberg-modellering" användes för att identifiera vilka dagvattenrelaterade ämnen som driver de observerade biologiska effekterna.

Provtagningspunkter nedströms dagvattenutsläpp uppvisade förhöjd biologisk aktivitet, särskilt kopplat till AhR-aktivering och oxidativ stress. Intressant nog noterades ökad ER-aktivitet främst vid uppströms punkter med låg urban påverkan och större inslag av jordbruk. Iceberg-modelleringen indikerade att flera högmolekylära PAH:er, såsom benzo[k]fluoranten, potentiellt kan bidra till effekter inom flera av de analyserade verkningsmekanismerna. Resultaten antydde även att 4-tert-oktylfenol teoretiskt skulle kunna påverka främst ER- och Anti-AR-respons. För vissa PFAS visade modelleringen platsberoende potentiella bidrag; vid NrkC föreslogs exempelvis att FOSA kan stå för en del av den beräknade Anti-AR-aktiviteten. I ett enskilt fall (NrkA) var PFOA den enda substans som bidrog till den kemiskt beräknade Nrf2-effekten, men detta utgjorde endast en mycket liten andel av den observerade bioaktiviteten.

Resultaten understryker att urbant dagvatten är en transportväg för biologiskt aktiva föroreningar till recipienter, och att detta vidgar perspektivet bortom vad riktade kemiska analyser ensamma kan avslöja.

Stormwater runoff transports organic contaminants from urban areas to receiving water bodies, yet its contribution to these pollutants in the aquatic environment is still poorly understood. Additionally, contaminants behave differently in receiving waters, with some binding to particles and accumulating in sediments while others stay dissolved in the water. This study was carried out three Swedish urban streams receiving stormwater discharges through separate sewer systems, under dry and wet weather conditions. Stream water and bottom sediment samples were collected along an urbanization gradient, from rural upstream to urban downstream sections, and analyzed for 50 stormwater-related organic contaminants to assess the impact of stormwater on contaminant levels. Polycyclic aromatic hydrocarbons (PAHs) and phthalates were more prevalent in sediment samples, with concentrations increasing along the urbanization gradient, indicating contributions from urban areas and stormwater runoff. In contrast, organotin compounds and phenols showed no clear pattern indicating transport through stormwater runoff in the water phase. Per and polyfluoroalkyl substances (PFAS) behaved differently from other contaminant groups by exhibiting a clear contribution from stormwater runoff in both phases. Though carried out in streams passing through relatively small urban settings, the findings clearly demonstrate that stormwater discharges can impact receiving waters. Of the 50 analyzed contaminants, three exceeded toxicity-based limits in dry weather (DW), seven in wet weather (WW), and twenty in bottom sediments. In the water phase, under DW and WW conditions, the three contaminants with the highest exceedance of toxicity-based limits were Perfluorooctanesulfonic acid (PFOS), Tributyltin (TBT), and 4-nonylphenol (4-NP). In the sediment phase, 4‑tert-octylphenol (4-t-OP), Tributyltin (TBT), and di-2-ethylhexyl phthalate (DEHP) were the three compounds with the highest exceedance of toxicity-based limits. Compared to relatively hydrophilic contaminants (e.g., PFAS), hydrophobic organic contaminants, particularly those accumulating in sediments (e.g. phenols, phthalates), posed a greater risk to the aquatic environment with exceedance levels reaching up to 105 times the thresholds. These findings raise concerns about the long-term impact on aquatic environments and highlight the need for mitigation strategies, including regulatory or operational restrictions on the contaminant sources and implementation of stormwater treatment facilities.

Per- and polyfluoroalkyl substances (PFAS) are extensively used in urban environments and are, thus, found in urban stormwater. However, the relevance of stormwater as a pathway for PFAS to urban streams is largely unknown. This study evaluated the impact of urban stormwater runoff on PFAS concentrations and spatial distribution in three urban streams affected by stormwater discharges from separate sewer systems. River water was sampled during dry (DW) and wet weather (WW) upstream, immediately downstream, and further downstream of three urbanized areas with separate sewer systems and with and without point sources (i.e. waste water treatment plant, airports). Water samples were analyzed for 34 targeted PFAS compounds and sediment samples for 35 targeted PFAS and 30 PFAS compounds using a total oxidizable precursor assay. The sum of the quantified PFAS concentrations ranged from the reporting limit (RL) to 84.7 ng/L during DW and increased as the streams were affected by WW discharges (0.87 to 102.3 ng/L). The highest PFAS concentrations were found downstream of urban areas and/or point sources (i.e. airports) during WW, indicating a clear contribution from stormwater discharges. A consistent PFAS contribution from the WWTP was observed under both DW and WW conditions. During WW events, concentrations of perfluorooctanesulfonic acid (PFOS) and total PFAS (PFOA equivalents) exceeded the annual average environmental quality standards, which are an established limit of 0.65 ng/L for PFOS and a proposed limit of 4.4 ng/L for total PFAS. Notably, except for the legacy PFAS, PFOS and perfluorooctanoic acid (PFOA), the most frequently quantified PFAS during DW were short-chain. For WW, long-chain perfluorocarboxylic acids (PFCAs) and a precursor, 6:2 Fluorotelomer sulfonic acid (6:2 FTS), were more frequently quantified, suggesting stormwater is a source of these longer-chain and particle-associated PFAS. The detection of unregulated fluorotelomer sulfonates (FTSs) such as 6:2 and 8:2 FTS during WW suggests a need for regulatory action, as these compounds can degrade into more stable PFAS. In sediment, higher concentrations, and a greater variety of PFAS were found at sites with known point sources i.e. airports. Long-chain PFCAs (C7–C13), perfluoroalkyl sulfonates (PFSAs) (C6), and precursors (i.e. N-Ethyl perfluorooctane sulfonamidoacetic acid), were more prevalent in sediments than in the water. Notably, PFOS concentrations in sediment exceeded the lowest Predicted No-Effect Concentration (PNEC) across sites, posing a potential long-term environmental risk, though current PNECs for other PFAS may underestimate such risks. The findings of the study highlight urban stormwater as a source of PFAS to urban streams indicating the need to minimize PFAS sources in the urban environment and to effectively treat stormwater to protect receiving water bodies.

Blue-green infrastructure (BGI) options are considered to be more sustainable practices for water management and bring arange of benefits over and above water management. Davidshall in Malmö, Sweden, has been used as a case area toassess the multiple benefits of implementing BGI, considering seven alternative BGI schemes systematically developed alongtwo scales: naturalness (i.e. more/less engineered/complex) and spatial distribution (e.g. decentral vs. end-of-pipe). The baseline alternative was the existing situation. The Benefit Estimation Tool (B£ST) was used to carry out a socio-economicassessment. The overall benefits varied significantly (two orders of magnitude), depending on the BGI scheme implemented:the greatest values were associated with natural decentral, natural decentral/end-of-pipe, and engineered decentral/endof-pipe alternatives, those including sub-surface and open dry detention, stormwater tree pits, and rain gardens. The threeB£ST categories providing the greatest benefits were enhancing amenity, benefiting health, and reducing flooding. Cultural ecosystem services were provided by all alternatives, and two alternatives (natural decentral and natural decentral/end-of-pipe)also provided regulating ecosystem services. The study showed that amenity and health were the most significant benefitsof BGI implementation, contrasting with the main aim of BGI implementation, which was stormwater management (water quality and flood protection).