Källor till och flöden av ftalater och nonylfenoler i Stockholms dagvatten
SEWSYS is a computer model designed for simulating fluxes of pollutants from its’ sources to the urban stormwater system. The model is able to simulate concentrations of substances in stormwater – thereby reducing the need for sampling and analyses of stormwater – as well as establishing the major sources of the pollutants in the urban environment. The aim of this work has been to identify the sources of some selected organic pollutants, adjusting SEWSYS to these new substances and simulating their fluxes in urban stormwater. The simulation results have then been used to investigate proper barriers to prevent these substances to reach the environment.
The prioritised pollutants chosen to be studied were four phthalates – DBP, DEHP, DINP and DIDP – nonylphenols (NP) and their ethoxylates (NPE). Phthalates are plasticisers used in PVC (often as coil coating), paint and sealants. NP/E:s are surfactants used in a range of materials, such as concrete, paint and plastics. In order to add these pollutants into the SEWSYS model, the emission of each substance from each of the identified sources was scrutinised. Depending on the overall lack of data, assumptions and estimations were necessary to be made for the emission calculations.
Two housing areas and one area dominated by traffic were selected for the modelling. Information on the prevalence of the different sources together with rainfall data were used for the simulation of stormwater runoff and pollution load. The model was calibrated with measured stormwater flows and volumes, as well as analysed concentrations of the pollutants in stormwater from the chosen housing and traffic areas. The traffic area showed high concentrations of phthalates in the stormwater samples. DIDP, and particularly DINP, showed the highest concentrations in most samples, both from the traffic area and the housing areas. The NP and NPE concentrations in most samples were close to or under the detection limits for the analytical methods used.
The calibration of the model showed that the runoff module in SEWSYS is able to predict the runoff volume well. After recalculating and adjusting some of the emission factors, the concentrations of the pollutants were in the same magnitude as the measured values. The simulations showed that vehicles are the dominating source of the phthalates in the traffic area. Parking spaces and concrete are indicated to emit significant amounts of NP/E:s. In the housing areas the construction materials – such as plastic coated steel for roofing and cladding – were the most important sources of phthalates. Parking spaces tend to cause high pollution loads of NP/E:s.
To reduce the load of organic pollutants in the environment a combination of barriers can be used – these barriers may include legislative measures to prohibit the use of a substance, recommendations to the consumers (not) to use specific construction materials or installing technical measures such as sedimentation facilities. A preliminary simulation show that by using construction materials free from phthalates or NP/E:s or reducing the traffic load, combined with a technical barrier such as a sedimentation pond, the pollution load from housing or traffic area is considerably decreased.