Stormwater runoff is a significant environmental issue, particularly in urban areas where impervious surfaces such as roads, rooftops, and pavements dominate the landscape. As rainwater runs off these surfaces, it picks up various pollutants, including heavy metals, before entering streams, rivers, and other waterways. Heavy metals are a particular concern due to their potential health impacts on humans and wildlife. Common metals in urban stormwaters, with their effects and sources are listed below:
- Zinc (Zn): Zinc is an essential nutrient for humans and animals, but it can be toxic in high concentrations. It can come from sources such as vehicle exhaust, galvanized metals used in infrastructure, and industrial activities.
- Copper (Cu): Copper is an essential nutrient for humans and animals, but it can be toxic in high concentrations. It can come from sources such as brake pads, electrical wiring, and industrial activities.
- Lead (Pb): Lead is a toxic heavy metal that can affect the nervous system, kidneys, and reproductive system. It can come from sources such as old paint, lead pipes, and vehicle exhaust.
- Cadmium (Cd): Cadmium is a toxic heavy metal that can affect the kidneys, bones, and respiratory system. It can come from sources such as industrial activities, batteries, and cigarette smoke.
- Mercury (Hg): Mercury is a toxic heavy metal that can affect the nervous system and kidneys. It can come from sources such as coal-fired power plants, industrial activities, and improperly disposed fluorescent light bulbs.
The cars, industries and metal parts in buildings and other infrastructure are the most common source of heavy metal for urban waters. Construction activities that expose soil and sediment which release heavy metals into stormwaters can also contribute.
Legislation in Europe and Finland
There are several European Union (EU) directives and regulations that address urban stormwater management and pollutant discharge. The Water Framework Directive (WFD) sets out a framework for the protection of surface waters, including urban stormwater, and requires member states to take measures to prevent or reduce the discharge of pollutants.
The Urban Waste Water Treatment Directive (UWWTD) also requires member states to treat urban wastewater and ensure it is discharged into surface waters with no harmful effects on human health or the environment. European Commission is currently working on the revision of the UWWTD to include requirements for the management of stormwater in it.
In many EU countries, the responsibility for monitoring and handling urban stormwater lies with the local or regional authorities, such as municipalities or water management agencies. These entities are responsible for implementing measures to reduce the discharge of pollutants from urban areas, such as green infrastructure, stormwater detention and treatment systems, and best management practices for construction sites.
In Finland, it is the responsibility of industrial and construction operators to manage waters that may be contaminated, with the Centre for Economic Development, Transport, and the Environment overseeing compliance with regulations. Meanwhile, cities and municipalities are responsible for stormwater management in general, although routine water quality monitoring for these waters is currently not in place.
Fast on-site metal analysis for Kuopio storm waters
Recently, 3AWater conducted several studies on stormwater quality in Kuopio, their hometown in Finland. In the spring of 2022, we visited a local stormwater clarification pond to take some product photos, but were surprised to find an elevated concentration of Zn (zinc) at 186 µg/l. Later that same summer, we were hired by Savonia University of Applied Sciences to conduct a brief stormwater survey on a rainy day. During this survey, we discovered a Zn concentration of approximately 450 µg/l in the drain that carries rainwater from the city center. Please refer to the map below to see the locations where sampling was conducted.
The Zn concentration values detected in the stormwater samples collected from Kuopio hold significant implications. Stormwater qualities are typically categorized according to the concentration guidelines set by Stockholm County in Sweden [1], as illustrated in the table below. The Zn concentration found in the city center was high, while the stormwater pond showed a medium Zn concentration. Additionally, Stockholm County has established specific guidelines for stormwater based on where the water is discharged [2]. For example, the guideline limit for Zn concentration in stormwater that drains into a large lake or sea is 125 µg/l. Both measured concentrations in Kuopio exceeded this limit, indicating a potential environmental risk.
The typical regulatory limit for a single sample concentration of Zn from the discharge water from an active mine is around 500 µg/l [3]. Therefore, the observed Zn concentrations are significant, and the discharge water from the city center almost exceeded the regulatory value for an operational mine. These findings raise questions about how much Zn is being released from the city area to the nearby Kallavesi lake and why it is not being continuously monitored and regulated.
It is important to note that these are just a few water samples analyzed from the Kuopio area, and a more comprehensive study should be conducted to draw clear conclusions. Nonetheless, the findings underscore the need for ongoing monitoring and regulation of stormwater in urban areas to prevent potential harm to the environment.
References:
[1] Klassificering av dagvatten och recipienter samt riktlinjer för reningskrav- del 2, Dagvattenklassificering by Stockholm Vatten och Avfall.
https://www.stockholmvattenochavfall.se/globalassets/pdfer/rapporter/dagvatten/dagvattenklassificeringdel2.pdf
[2] Förslag till riktvärden för dagvattenutsläpp by Regionala dagvattennätverket i Stockholms Län.
https://static1.squarespace.com/static/592c525fe3df282718f63597/t/5e05bb3b966a241ee2c7dff6/1577433916644/Riktvarden_dagvatten_feb_2009.pdf
[3] TERRAFAME OY VESIPÄÄSTÖJEN TARKKAILU 2021 by Eurofins Ahma Oy
https://www.terrafame.fi/media/naapureille/ymparistotarkkailuraportit/2021/03-terrafame_tarkkailu-2021_vesipaastot.pdf