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Impact of road runoff in soil and groundwater. Synthesis of Portuguese and other European case-studies TERESA E. LEITÃO PhD in Hydrogeology, Senior Research Officer at National Laboratory for Civil Engineering [email protected] Groundwater Division of DHA/LNEC Av. do Brasil, 101, P-1700-066 Lisboa, Tel. (+351) 21 844 3802 http://www.dha.lnec.pt/nas Abstract Road circulation is capable of producing compounds that can pollute the environment. The level and type of emissions depend on several technical aspects that can be related with the road design and the vehicle engineer (size, type of fuel used), as well as with operational factors that are related with the way that the vehicle is used. The compounds emitted come from the fuel combustion, vehicle compounds use, road accessories (like lateral crash barriers) degradation, road degradation, maintenance procedures (application of chemicals), leakage, and accidents. In this paper a synthesis of soil and groundwater pollution by heavy metals in the vicinity of roads is presented. The results are based on data collected by LNEC as well as other data gathered in published papers, summing more than three dozens of case-studies in 10 different European countries. The objective of this analysis was to compile as much information as possible about road pollution by heavy metals in soil and groundwater, in order to be able to have a general overview for Europe of the effective degree and extension of road pollution, independently of the different conditions specific of each study area. Key Words: road pollution; soil; groundwater; European case-studies. INTRODUCTION Traffic is a source of diffuse pollution with impacts in the environment that need to be prevented or minimised. Cars, lorries, motorcycles, among other vehicles, are emitting heavy metals (Pb, Zn, Fe, Cu, Ni, Cd, Hg, Cr), hydrocarbons (PAH, oil, fuels), nutrients (N, P), particulates (clay and soil particles) and other organic matter (dust, dirt, humus) into the environment (Table 1). 1 Table 1 Overview of pollutants originating from roads and traffic and their main sources (adapted from Gupta et al., 1981a; Luker and Montague, 1994, and Leitão et al., 2000) Type of pollutant Heavy metals Cadmium Chromium Copper Lead Zinc Hydrocarbons PAHs Nutrients Organic matter Salts Microbe Particulates Source of pollution Tyres and brake pads, fuel, motor oil additives, rust, crash barriers Tyres, brake pads Bearing, tyres, brake pads Tyres, brake pads, radiators Fuel, tyres, brake pads Lubricating oils, tyres, brake pads, crash barriers Oils, fuels, exhaust emission Fuel, plastics, pavement Fertilizers, motor fuel & oils, exhaust emission Vegetation, litter, animal droppings De-icing and fertilizers Soil, litter, excreta, livestock movements Tyre, brake & pavement wear, mud & dirt accumulated on vehicles The quantification and control of diffuse pollution sources is a requirement of the Water Framework Directive, which states that member-states should address the water policy issues in a coherent, holistic and sustainable approach. The mechanisms and pathways through which diffuse pollutants from roads move through the environment are important considerations in planning and targeting prevention and control measures. The results presented hereinafter are a part of the information collected in case studies analysed in LNEC since 1997, in the framework of EU studies, together with other information collected in published papers. They refer to the knowledge gathered for the case of heavy metals pollution dispersion in soils and water, in more than 3 dozen of case-studies, in 10 different European countries. IMPACTS OF HEAVY METAL ROAD POLLUTION IN THE SOIL AND WATER The majority of studies on heavy metals in road runoff have concentrated on lead, cadmium, copper, zinc and iron. Some studies have also included nickel, chromium and manganese. The more unusual metals, such as titanium, vanadium, cobalt, arsenic, molybdenum, tin, tungsten 2 and antimony, are occasionally mentioned as trace constituents (James, 1999). Metals in runoff can be attached to inert sediments, or be contained in immiscible fluids, or occur as particles, soluble salts or insoluble compounds. Chemically they can be organic or inorganic, compounds or complexes, and can usually exist amongst a variety of ionic species depending primarily on the prevailing redox and pH conditions. Soil is the media where the road pollution history is kept. Groundwater is a more hydrodynamic media, subject to higher quality fluctuations over time, depending on permeability properties of the media as well as chemical properties such as pH and CEC. Heavy metals can be harmless in minute quantities. However, at high concentrations biological life can be threatened. The following text presents some of the results gathered for the studied heavy metals. Cd is a very mobile element and the metal that more easily desorbs by ionic exchange processes (Harrison et al., 1981; DWW, 1995; Reinirkens, 1996; Leitão et al., 2000, Pagotto et al., 2001 & Diamantino, 2002). The presence of Cd in soil and groundwater close to the roads is usually low, in concentrations lower than the intervention1 and VMA2 defined, respectively. Nevertheless, its presence due to road effects is clear (Fig. 1). In most case-studies the Cd concentration decreases with distance to the road, and in several cases also with depth 1 For soil, the quality values used are defined in Dutch legislation (MHSPE, 1994) as target and intervention For groundwater, the quality values used are defined in Portuguese legislation (DL 236/98, 1998) as recommended (VMR) and admissible (VMA) 2 3 Cd (mg/kg) variation in soils close to the road, at 3 distances and 3 depths Variação de Cd (mg/kg) em solos adjacentes a estradas, a 3 distâncias e 3 profundidades Intervention value Valor de Intervenção (12 mg/kg) (12 mg/kg) 12 - 37 countries (P,SP,F,I,D,SW,NL,DK,UK,FIN) - 37study casoscases;10 de estudo; 10 países (P, SP, F, I, D, SW, NL, DK, UK, FIN) -- max. máx upper quartile quartil sup. 8 median mediana lower quartil inf.quartile mín. min. 4 Target value Valor guia (0.8 mg/kg) (0,8 mg/kg) 0 -1 m 1-5m 2-10 cm prof. depth 0-2 cm depth prof. 10-30 cm depth prof. 2-10 cm prof. depth 0-2 cm depth prof. 10-30 cm depth prof. depth 2-10 cm prof. 0-2 cm depth prof. 0 20 - 30 m Fig. 1 Cd variation in soils close to the road, at 3 distances and 3 depths Cd presence can also be observed in the groundwater and interstitial water in the vicinity of roads. It is possible to observe clear variations along the time and with distance to the road, due to its high mobility, with some few samples exceeding the target value (Fig. 2). It is possible to notice an increase of concentration after rain events. Cd concentration in the road vicinity is not high once its initial amount in road dust is low. Therefore, even if there are changes in the soil conditions (e.g. pH decrease) that promote Cd mobility, it is not likely to find high Cd concentrations. Nevertheless, it is important to be acquainted about Cd toxicity at very low levels and about its cumulative characteristics. 4 5 Cd (µ µg/l) 4.5 July - Sept. 98 Oct. - Dec. 98 Jan. - Mar-99 April - Jun-99 4 3.5 3 VMA = 5 µg/l (6 µg/l) VMR = 1 µg/l (0,4 µg/l) 2.5 2 (Dutch legislation 1.5 MHSPE, 1994) 1 0.5 P, Vila Real, IP4 P, Recta do Cabo, EN10 F, Erdre, A11 F, Houdan, RN12 D, Rud, M70 Fin, Utti, VT6 D, Vejenbrod, M14 Fin, Lohja, VT25 SE, Norsholm, E4 SE, Svaneberg, E20 NL, Spaarnwoude, A9 NL, Nieuwegein, A2 UK, Reading, M4 UK, Oxford, M40 0 Fig. 2 Cd concentration in groundwater Cr is a metal that tends to accumulate in the soils due to its low mobility. Its presence in areas far from the road denotes atmospheric pollution (Ward, 1990a). Variação de Cr (mg/kg) em solos adjacentes a estradas, a 3 distâncias e 3 profundidades Cr (mg/kg) variation in soils close to the road, at 3 distances and 3 depths - 26study casos cases;10 de estudo; countries 10 países (P, SP, F, I, D, SW, NL, DK, UK, FIN) - 26 (P,SP,F,I,D,SW,NL,DK,UK,FIN) - 400 Valor de Intervenção Intervention value (380 mg/kg) (380 mg/kg) max. máx upper quartile 300 quartil sup. median mediana lower quartil inf.quartile . mín min. 200 Valor guia 100 Target value (100 mg/kg) (100 mg/kg) 0 -1 m 1-5m depth 2-10 cm prof. 0-2 cm depth prof. depth 10-30 cm prof. 2-10 cm depth prof. 0-2 cm depth prof. 10-30 cm depth prof. 2-10 cm prof. depth 0-2 cm depth prof. 0 20 - 30 m Fig. 3 Cr variation in soils close to the road, at 3 distances and 3 depths 5 Cr concentrations in the soils of 26 case-studies are below intervention values defined in Dutch legislation. Nevertheless, the target value is frequently overcome. In some of the case-studies it is possible to observe the decrease in Cr concentration with the distance to the road and in depth, but other cases show the opposite pattern. Usually Cr concentration is quite constant along the depth and distance showing a low capacity for mobilization to the groundwater (cf. Fig. 3). This is also evidenced by the low concentration of Cr in water (all lower than 5 µg/l). Fig. 4 shows the concentration found in the vadose zone water. Groundwater concentration for the same studies show concentrations above detection limit in few cases. 50 Cr (µ µg/l) 45 40 VMA = 50 µg/l (30 µg/l) VMR = - (1 µg/l) 35 (Dutch legislation, 30 MHSPE, 1994) 25 20 15 10 5 3.9 0.8 15 - 40 m 0.00 1-5 m 0-1 m P, Vila Real, IP4 Fin, Utti, VT6 D, Vejenbrod, M14 Fin, Lohja, VT25 SE, Norsholm, E4 SE, Svaneberg, E20 NL, Spaarnwoude, A9 UK, Oxford, M40 NL, Nieuwegein, A2 UK, Reading, M4 2.5 F, Houdan, RN12 0.7 P, Recta do Cabo, EN10 1.1 1.8 D, Rud, M70 3 0 F, Erdre, A11 5 April - June 99 Jan - March 99 Oct - Dec 98 July - Set 98 Fig. 4 Cr concentration in the vadose zone Cu is a low mobility metal, especially in areas with some organic matter content, not significantly influenced by changes in pH or salt content. It is one of the metals found connected to road pollution (DWW, 1995; Reinirkens, 1996; Leitão et al., 2000 & Diamantino, 2002). Cu concentration in the soils analysed are frequently above the target value, specially in the first soil horizon and close to the road. However the intervention value is unusually 6 overcome (cf. Fig. 5). It is also clear the decrease of Cu with distance and depth in several case-studies individually. Variação de Cu (mg/kg) em solos adjacentes a estradas, a 3 distâncias e 3 profundidades Cu (mg/kg) variation in soils close to the road, at 3 distances and 3 depths casos de estudo; 10 países (P, SP, F, I, D, SW, NL, DK, UK, FIN) -- 37- 37 study cases;10 countries (P,SP,F,I,D,SW,NL,DK,UK,FIN) 240 200 Valor de Intervenção Intervention(190 value mg/kg) (190 mg/kg) 160 max. máx upper quartile quartil sup. median mediana 120 lower quartile quartil inf. mín. min. 80 Target value (36 mg/kg) Valor guia (36 mg/kg) 40 0 -1 m 1-5m depth 2-10 cm prof. depth 0-2 cm prof. depth 10-30 cm prof. 2-10 cm depth prof. 0-2 cm depth prof. depth 10-30 cm prof. depth 2-10 cm prof. depth 0-2 cm prof. 0 20 - 30 m Fig. 5 Cu variation in soils close to the road, at 3 distances and 3 depths 80 Cu (µ µg/l) 86 70 60 VMA = 50 µg/l (75 µg/l) VMR = 20 µg/l (15 µg/l) 50 (Dutch legislation, MHSPE, 1994) 40 33 30 23 20 10 15 - 40 m 1-5 m P, Vila Real, IP4 P, Recta do Cabo, EN10 F, Houdan, RN12 D, Rud, M70 0-1 m F, Erdre, A11 Fin, Utti, VT6 D, Vejenbrod, M14 Fin, Lohja, VT25 SE, Norsholm, E4 SE, Svaneberg, E20 NL, Spaarnwoude, A9 UK, Oxford, M40 NL, Nieuwegein, A2 UK, Reading, M4 0 April - June 99 Jan - March 99 Oct - Dec 98 July - Set 98 Fig. 6 Cu concentration in the vadose zone 7 Concerning the Cu water concentration, several values are higher than VMR, but all except one are below VMA. The higher values are closer to the road (cf. Fig. 6). Pb is one of the metals more studied under road pollution. Soil analysis during the last 25 years has shown changes in the decrease of Pb due to the consumption of unleaded gasoline. Pb mobility is dependent on the presence of carbonates, Fe-Mn oxydes and to organic compounds. Their presence favours the Pb accumulation in the soil and limits its capacity to be leached (DWW, 1995). Pb (mg/kg) variation in soils close to the road, at 3 distances and 3 depths Variação de Pb (mg/kg) em solos adjacentes a estradas, a 3 distâncias e 3 profundidades 1000 - 37 casos de estudo; 10 países (P, SP, F, I, D, SW, NL, DK, UK, FIN) - - 37 study cases;10 countries (P,SP,F,I,D,SW,NL,DK,UK,FIN) - 800 max. máx upper quartil sup. quartile lower quartile mediana median 600 quartil inf. mín. min. Intervention value Valor de Intervenção (530 mg/kg) (530 mg/kg) 400 200 Target value (85 mg/kg) Valor guia (85 mg/kg) 0 -1 m 1-5m 10-30 cm depth prof. 2-10 cm prof. depth 0-2 cm depth prof. depth 10-30 cm prof. 2-10 cm prof. depth 0-2 cm depth prof. 10-30 cm depth prof. depth 2-10 cm prof. 0-2 cm prof. depth 0 20 - 30 m Fig. 7 Pb variation in soils close to the road, at 3 distances and 3 depths In most case-studies, the Pb concentration in soils is quite high, several exceeding the intervention value. For waters, the presence of Pb is clear, but below VMA. In most case-studies it is observed a diminution of Pb with the distance to the road and in depth (cf. Fig. 7). In 10 of the 14 case-studies analysed under POLMIT project, the water in the vadose zone had concentrations below 10 µg/l. In some places there are significant changes during the 8 year. Also groundwater has concentrations below VMA, and the pattern of concentrations is very dependent of soil conditions (cf. Fig. 8). 50 Pb (µ µg/l) 45 July - Sept. 98 Oct. - Dec. 98 Jan. - Mar-99 April - Jun-99 40 35 30 25 VMA = 50 µg/l (75 µg/l) VMR = (15 µg/l) 20 15 (Dutch legislation 10 MHSPE, 1994) 5 P, Vila Real, IP4 P, Recta do Cabo, EN10 F, Houdan, RN12 D, Rud, M70 F, Erdre, A11 D, Vejenbrod, M14 Fin, Utti, VT6 SE, Norsholm, E4 SE, Svaneberg, E20 NL, Spaarnwoude, A9 NL, Nieuwegein, A2 UK, Reading, M4 UK, Oxford, M40 0 Fig. 8 Pb concentration in groundwater Zn is a very mobile element especially in sandy and acid soils. Pagotto et al. (2001) refers to a particular sensitivity of Zn to pH decrease, with a consequent mobilization of this metal. Zn concentration in soils is higher than the target value for the 3 depths and 3 distances analysed, in several case-studies (cf. Fig. 9). It is also clear a decrease in concentration with distance to the road and depth, although that is not the case in many individual case-studies. The existence of Zn in groundwater varies from case to case, depending on the existing physico-chemical conditions. Some authors found almost no evidence of Zn pollution (Reinirkens, 1996) but most Fig. 10 found the opposite. However, values are below VMA. 9 Zn (mg/kg) variation in soils close to the road, at 3 distances and 3 depths Variação de Zn (mg/kg) em solos adjacentes a estradas, a 3 distâncias e 3 profundidades casoscases;10 de estudo; countries 10 países (P,(P,SP,F,I,D,SW,NL,DK,UK,FIN) SP, F, I, D, SW, NL, DK, UK, FIN) - 37- 37study - 1000 800 Valor de Intervenção (720 mg/kg) Intervention value (720 mg/kg) máx max. upper quartil sup.quartile 600 mediana median lower quartil inf. mín. quartile min. 400 200 Target value Valor guia (140 mg/kg)(140 mg/kg) 0 -1 m 1-5m 2-10 cm prof. depth 0-2 cm prof. depth 10-30 cm depth prof. 2-10 cm prof. depth 0-2 cm prof. depth 10-30 cm prof. depth 2-10 cm prof. depth 0-2 cm prof. depth 0 20 - 30 m Fig. 9 Zn variation in soils close to the road, at 3 distances and 3 depths 500 450 July - Sept. 98 Oct. - Dec. 98 Jan. - Mar-99 April - Jun-99 400 350 300 250 VMA = 3000 µg/l (720 µg/l) VMR = 500 µg/l (140 µg/l) 200 150 (Dutch legislation MHSPE, 1994) 100 50 P, Vila Real, IP4 P, Recta do Cabo, EN10 F, Houdan, RN12 F, Erdre, A11 D, Rud, M70 D, Vejenbrod, M14 Fin, Utti, VT6 SE, Norsholm, E4 SE, Svaneberg, E20 NL, Spaarnwoude, A9 UK, Oxford, M40 NL, Nieuwegein, A2 0 UK, Reading, M4 Zn (µ µg/l) Fig. 10 Zn concentration in groundwater 10 SYNTHESIS AND CONCLUSIONS Road pollution is a source of diffuse pollution that can affect the soil and water in its vicinity. The effects of runoff discharge in the environment usually do not led to acute pollution effects. The long term effects, namely of heavy metals, are the ones that can cause soil and water degradation. The 37 case-studies analysed have shown the long term effects of heavy metals road pollution in soils. The direct effects of road pollution are spatially limited to the soils adjacent to roads, in the areas of car splash, usually influencing a strip narrower than 25 m (García e Millán, 1994; Reinirkens, 1996). However, other authors (Ward e Savage, 1994) confirm a significant increase of soil metal content up to 100 m from the road (London M25). In most cases, heavy metal pollution decreases with the distance to the road (García e Millán, 1994). Also the first soil horizon is the more polluted one in term of heavy metals (cf. Ward, 1990a). Road pollution is dependent of the traffic level but a direct correlation is not possible due to the influence of other factors such as wind direction, precipitation pattern, age of the road, topography, pH, CEC, soil organic matter content, etc. Among the main heavy metals causing pollution are Pb, Zn and Cu. Ni and Cr do not influence in a relevant way the soil quality in the areas close to the roads. Several other heavy metals are under study at the present. Cd, being a mobile element, is produced in low concentrations. Pb and Cu are produced in higher quantities but their mobilization is difficult; only for low pH conditions or as a soluble complex it is possible to mobilize them in a significant way. Zn is emitted in considerable quantities, especially when zinc crash barriers exist, and can be very mobile in acid conditions. 11 REFERENCES Campo G., Orsi M., Badino G., Giacomeli R. & Spezzano P. (1996) Evaluation of motorway pollution in a mountain ecosystem. 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