Vol. 4: Effect of road traffic on heavy metal concentrations of plants Toivo Yläranla Agricultural Research Centre ofFinland, Institute ofSoils and Environment, FIN-31600 Jokioinen, Finland The concentrations of zinc, copper, lead, cadmium and nickel in spring wheat grain and straw, Italian rye grass and lettuce were studied in a two-year field experiment conducted alongside two roads with a daily traffic density of 9500 and 5500 vehicles each. The experimental plots were located 22, 58 and 200 m from the roads. As controls, polyethylene pots filled with non-contaminated soil were placed in each plot. The values for the bulk deposition of lead were 50% and those for dry deposition over 50% higher in the plot 22 m from the roadside than in the plot 200 m from the roadside. The bulk deposition of zinc also decreased slightly with distance from the road. Cadmium depositions were low at all experimen- tal sites. The highest values for dry deposition of lead and cadmium were recorded when the wind blew from the road in the direction of the collectors. The heavy metal concentrations varied from plant to plant but for a particular species were similar at different experimental sites. The highest zinc, cadmium and nickel concentrations were measured in lettuce. The lead concentration of wheat straw, Italian rye grass and lettuce at 22 m from the roadside was 1.5-3 times that of the background level at 200 m. In wheat grain, the lead concentration was very low and did not change with distance from the road. The plants took up lead mainly from air deposition. The zinc concentration of wheat grain and the nickel concentration of Italian rye grass were also high. Cadmium concentrations were low in wheat grain and straw and in rye grass. In wheat, the zinc and copper concentrations were higher and the lead and cadmium concentrations much lower in grain than in straw. Key words: pollution, bulk deposition, dry deposition ntroduction The worldwide use of lead alkyls in petrol since 1923 has led to average lead emissions in the northern hemisphere of about 20 mg nr2 (Wick- ern and Breckle 1983). In 1988, estimated lead emissions in Finland totalled47 400 kg, ofwhich 76% was due to road traffic (Aunela and Lar- java 1990). Some other heavy metals, e.g. zinc, copper, cadmium and nickel, are also spread by road traffic (Lagerwerff and Specht 1970, John- © Agricultural Science in Finland Manuscript received May 1994 35 AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=RxmaA_PpkSkKEFGm.qBoGv7yyJm08l13piF3LpQ.LJwxuwcJahadZIVFwQ7YxhwCWXjeWCQgBtrRlOCHfO_iX0y8iYs25afXe6WB1nlq_Fda0yrBdUdtScyjaPGVjCoUwKiP_P3_UJxyp6PAfanng4cEgx2xyl0EOLOqca13ZH3np_y-1k-todyPbDznw87_Luc1Yq35uWC7pmCnXK5p1ex1xn0APnirv0HUrfbNqT_gyVE5y34Q9DPi3nEP9_as_6NfFs9cr11RwnZK1JicejYIiA_AAcPvBaQbI6j4n1DfuYY0aFtgcA ston and Harrison 1984, Albasel and Cottenie 1985, Ho and Tai 1988). Lead is not generally considered an essential microelement for either animals or humans. Its importance as an object of study is based on its toxicity when present in above-normal concentrations. Cadmium, howev- er, may be benefical to animals in very small amounts (e.g. Anke et al. 1986). Zinc and cop- per are essential elements for plants and animals; so is nickel, as shown by some studies (Eskew et al. 1984). Plants do not have ion-selective systems to prevent themfrom taking up elements if these are available. Thus they always contain both essential and harmful elements and so are useful indicators of pollution. The heavy metal concentrations ofcrops vary widely from one crop to another. Considerable differences also exist between the heavy metal concentrations of various parts ofplants (Yläran- ta and Sillanpää 1984,Sillanpää et al. 1988, Sil- lanpää and Jansson 1991). Yläranta and Sillan- pää (1984) measured the lowest copper concen- tration in the underground parts of some root crops and in the straws of grain crops. A fairly high zinc concentration was typical of grains. The lowest average lead concentration was de- termined on those plant parts which had been exposed to either no or limitedexternal contam- ination by air. Considerably higher lead concen- trations were found in crops or their parts in which exposure to air had been greater due ei- ther to their larger surface area or to a longer growth period (Sillanpää et al. 1988). Percent- ages as high as 90 or more of lead in plants are thought to derive from airborne lead (Tjell et al. 1979) In general, cereal grains were low in cad- mium. The most effective cadmium collectors were root crops (Sillanpää and Jansson 1991). The mean concentration of soluble lead in Finnish agricultural soils is higher than that of soluble nickel (Sippola and Tares 1978, Paasikal- lio 1978). In plants, however, the nickel concen- tration is higher than that of lead (Paasikallio 1978, Syvälahti and Korkman 1978). The tendency for elementalconcentrations to be high- er in leaves than in non-foliar edible parts ap- plies to zinc, copper, lead and cadmium but not to nickel, which commonly has higher concen- trations in edible parts than in leaves (Davis and Carlton-Smith 1980). The aim of this study was to measure the concentration in plants of lead and some other elements that was due to airborne deposition, road traffic in particular. If the soil is contami- nated, it is not sufficient to measure the elemen- tal concentrations in soil and plants alone. There- fore, a special experimental technique was used in whichpots filled with “clean” soil were placed on the plots located at different distances from the road. The elemental concentrations of plants growing on the plots and in the pots were then compared in order to establish what proportion was due to air deposition. Methods Experimental fields The experiment was carried out in 1987 at two experimental sites in southern Finland: one by highway 3 at Nurmijärvi (NU, 60° 31' N, 23° 51' E) and one by highway 2 at Jokioinen (JO, 60° 53' N, 23° 28' E). In 1988, the experiment was carried out at Jokioinen only, and a field (JOK, 60° 4F N, 23° 21' E) located far from any busy roads was chosen as a reference site. To avoid contamination disturbances, the experi- mental sites were in locations without any emis- sion sources or natural obstacles in the vicinity. The road surface at Nurmijärvi was 2.5 m and at Jokioinen 2 m above the level of the adjacent experimental field. The roads were 6 m wide and asphalted. The road at Nurmijärvi runs from south to north and that at Jokioinen from south- east to northwest. Thus, at Nurmijärvi the fields were west of the road (90°) and at Jokioinen northeast (30°). The daily traffic density at Nur- mijärvi was 9500 and at Jokioinen 5500 cars. The main wind directions were southerly, south- easterly, westerly and northeasterly for the ex- perimental plots at Nurmijärvi as measured at 36 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect ofroad traffic on heavy metal concentrations ofplants Vol. 4: 35^8. Tuusula, about 15 km to the southeast of Nurmi- järvi, and southerly to westerly for Jokioinen, as measured in 1987 and 1988 at the meteoro- logical station 10 km to the southeast of the ex- perimental site. The experimental plots were lo- cated on arable land that had long been used for normal cultivation practices, mostly for grow- ing cereals. Plots, 3 x 3 m 2 in size growing spring wheat (Triticum aestivum, cv. Ruso), Australian lettuce (Lactuca saliva) or Italian rye grass (Lolium multiflorum L., cv. Amenda), were established at each experimental site (Fig. 1). The plots lay 22 m (JO I, NU I), 58 m (JO 11, NU II) and 200 m (JO 111, NU III) from the roadside, respectively. The plough layer (0-25 cm) of experimental soils (NU and JO) was heavy clay except at JOK, where it was sandy (Table 1). On JO and NU fields, the particle size distribution was finer in the deeper layer (30-60 cm) than in the plough layer. At JOK the deeper layer was clay soil. Pure HD polyethylene pots, 30 litres in ca- pacity, 42 cm in height and 30 cm in diameter, were placed on each plot. The pots were filled with sandy soil in 1987 (16.5 kg of dry matter) and with Carex peat in 1988 (7.0 kg of dry mat- ter). The bottom of each pot was covered with 8 kg of coarse quartz gravel (0 8-16 mm) to a height of 12 cm and topped with 3 kg of fine quartz gravel (0 3-5 mm) to prevent the pot soil from mixing with the coarse gravel. The quartz gravels were washed with 4 M HCI, and rinsed with tap water and finally deionized water until all acidity had been washed out. The gravels pre- vented the plant roots from growing from the pots into the soil. The fertilizers used annually were pure chem- icals (Merck, p.a.) dissolved in deionized wa- ter: N 100 kg ha ' (NH 4N0 3 , KN0 3 ) P3l kg ha 1 (KH,PO 4 ) K 80 kg ha 1 (KNO,, KH,P04 ) In 1988, magnesium (71 kg/ha) and sulphur (94 kg/ha) fertilization was also given as MgS04 x 7 H2 O. In both years, the fertilization in the pots was twice that in the plots. In the plots, the fertilization solution was placed at a depth of7 cm in 12rows 25 cm apart. The seed rows crossed the rows with fertilizer. Fig. 1.Schematic diagram of the experimental field. 37 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect ofroad traffic on heavy metal concentrations ofplants Table 1. Soil sample means of JO I—ol, NU I-111, JOK and pots for pH(CaCl 2 ), organic carbon content (OC, %) and particle size distribution (clay <0.002, silt 0.002-0.02, fine sand 0.02-0.2 and coarse sand 0.2-2 mm). Layer, Sand cm pH OC Clay Silt Fine Coarse JOI 0-25 5.6 4.0 68 17 9 6 30-60 6.0 0.5 80 9 10 1 JO II 0-25 5.1 3.4 69 16 9 6 30-60 5.8 0.6 84 6 8 2 JO 111 0-25 5.2 3.1 69 12 10 9 30-60 5.6 0.6 86 4 8 1 NU I 0-25 5.5 3.9 69 18 8 5 30-60 6.2 0.7 79 11 8 2 NU II 0-25 5.5 4.1 71 19 7 3 30-60 6.3 0.4 78 12 10 0 NU 111 0-25 5.8 3.8 74 18 6 2 30-60 6.3 0.4 78 10 10 2 JOK 0-25 6.3 2.8 26 16 35 23 30-60 6.3 0.6 48 21 25 6 Pot soils Sandy soil 5.8 6.1 5 6 62 27 Carex peat 6.0 37 - - Wheat (300 g) and Italian rye grass (10 g) were sown in 25 and lettuce (10 g) in 12 rows; wheat at a depth of 5 cm and Italian rye grass and let- tuce at a depth of 2-3 cm. In the pots, the fertili- zation and seed depths were about the same as in the adjacent plot. The amount of seeds sown in the pots was one-tenth of that sown in the plots. The plants were cut with stainless steel seis- sors, avoiding contamination by soil as far as possible. Thus, after being cut, the plant parts from nearest the soil were rinsed with deionized, ultra-pure water (Millipore Milli-Q Water pud- fication system). Lettuce was cut when the main growth had finished but the leaves were still fully green. Rye grass was cut at the silage stage (two yields in 1987 and three in 1988). Fertilization after the first cut was the same as that for the first cut but, in the pots, it was given in two lots 10 days apart. Spring wheat - both grain and straw - was harvested at the mature stage. The whole growth was harvested from each pot. A plant sample two to three times the size of the pot yield was harvested from the plot around each pot. Each plot sample consisted of six sub- samples. The samples were placed into paper bags and dried at 60°C. Finally, the plant growth on all plots was harvested and the dry matter yields were determined, Bilik and dry deposition Sampling Two NILU (Norsk Institut for Luftforskning, Lillestrpm, Norway) deposit gauges with 2-litre bottles, one for nitrogen, sulphur and phospho- rus (NSP) and one for the heavy metals zinc, copper, lead, cadmium and nickel (ME), were placed on each experimental field. The deposit gauges were of a funnel type with a cylindrical nylon mesh on the bottom of the funnel to pre- vent insects from getting trapped in the bottle. The HD polyethylene collectors were placed in a stainless steel frame at a height of 1.8 m (SFS 3865). Concentrated HN03 (4 ml, Merck Sup- rapur, Art. 441) diluted with 10 ml of deion- 38 Vol. 4: 35-48. ized, ultra-pure water was added to the bottle in- tended for heavy metal collection to prevent ab- sorption of the elements on the walls of the bot- tle. The bottles were emptied weekly or when the volume of water collected was sufficientfor el- emental analysis. The collector gaugewas rinsed with 50 ml of 0.1 M HNO, (ME) or 50 ml of ultra-pure water (NSP). The total volume of water in the collector bottle was then measured and the water transferred to an LD polyethylene bottle. In 1988, dry deposition was collected at JO I and JO 111 on a 47-mm teflon filter (Millipore FALPO47OO, pore size 1 pm) using a Nucleopore Swin-Lok douple holder adapter and TTL-1 dust collectors (Levy Ky, Helsinki, Finland). Sarto- rius PC membrane (SN; 111132,pore size 8 pm) was used as a prefilter for the Millipore FA fil- ter. The filters were changed twice a week. Dur- ing this time 100-200 m 3 of air was passed through the filters. Analytical methods The zinc, copper, lead, cadmium and nickel in the experimental soils were extracted with acid ammonium acetate-EDTA (HAAC-EDTA, Lakanen and Erviö 1971) and aqua regia (AR, 0.5 g soil boiled for 2 h in a mixture of 7.5 ml cone. HCI and 2.5 ml cone. HN0 3 , Kick et al. 1980) and analysed by ICP-AES (Zn, Cu) and ET-AAS (Pb, Cd, Ni). The zinc, copper, calci- um, magnesium, potassium and phosphorus con- centrations in the plant samples were determined with ICP-AES after dry ashing (Sillanpää and Jansson 1992); the sulphur concentration was determined after wet digestion by slightly mod- ifying the method of Huang and Schulte (1985). The concentrations of lead, cadmium and nickel in plant samples were determined with ET-AAS after dry ashing (Sillanpää and Jansson 1992). Total nitrogen in deposition was determined by oxidizing inorganic and organic nitrogen com- pounds into nitrate in alkaline solution. The ox- idation was done under pressure (200 kPa, 120°C) for 0.5 h. The nitrate concentration was determined by reducing the nitrate into nitrite in a copper-cadmium column according to the Finn- ish recommendation for the standard nitrate ni- trogen method (SFS 3031). The determination was done on NSP samples with an autoanalyser. Sulphur, phosphorus, zinc, copper and nickel were analysed on acidified ME samples (0.1 M HN0 3 , Merck Suprapur) with ICP-AES and lead and cadmium with ET-AAS. To determine the dry deposition of lead and cadmium, the teflon filters were cut into four pieces of equal size. The two crossing parts of each filter chosen for lead and cadmium analy- ses were digested in a teflon beaker, A mixture of 3 ml of concentrated HN0 3 (Merck Suprapur, Art. 441) and 0.75 ml of concentrated H 20 2 (Merck p.a. Art. 7209) was added to the beaker. The solution was evaporated to 1 ml on an elec- tricalplate and 3 ml ofconcentrated HCI (Merck Suprapur, Art. 318) was added. The solution was evaporated to just under 1 ml, and 10 ml ofMil- li-Q water was added. The beaker was left for 20 min. in a Branson Ultrasonic Cleaner with the heat button on. The solution was transferred quantitively into a 25-ml measuring flask. Lead and cadmium were analysed on the digestion solution with ET-AAS. Results and discussion Soil characteristics The concentrations of HAAC-EDTA-extractable zinc, copper, lead and nickel in the experimental soils were very low compared with the AR extract- able concentrations (Table 2). In contrast, one-third or more of aqua regia-extractable cadmium was also extractable into HAAC-EDTA. The results of the AR analyses confirmed the low zinc, copper, lead and nickel concentrations in coarse JOK and pot soil and also in Carex peat pot soil. The HAAC-EDTA-extractable copper, lead, cadmium and nickel concentrations in the plough 39 AGRICULTURAL SCIENCE IN FINLAND Table 2. Soil sample means for HAAC-EDTA and aqua regia-extractable Zn, Cu, Pb, Cd, Ni (mg/kg of dry soil). HAAC-EDTA AQUA REGIA Layer, Zn Cu Pb Cd Ni Zn Cu Pb Cd Ni cm JOI 0-25 1.3 7.4 5.5 0.10 2.1 148 50 34 0.19 55 30-60 0.8 4.8 3.9 0.04 2.0 JO II 0-25 1.47.1 4.50.12 1.8 159 49 34 0.21 44 30-60 1.15.0 4.10.02 2.4 JO 111 0-25 1.56.3 4.30.09 1.8 160 47 30 0.41 46 30-60 1.15.4 3.40.04 2.1 NUI 0-25 1.89.3 6.20.13 3.0 176 57 31 0.26 49 30-60 0.94.4 4.10.03 1.6 NU II 0-25 2.89.0 6.40.13 2.8 165 59 28 0.34 55 30-60 0.94.3 4.40.04 2,1 NU 111 0-25 1.38.8 6.30.11 2.7 188 58 24 0.30 69 30-60 1.34.4 4.20.04 2.9 JOK 0-25 2.54.5 2.60.09 1.0 82 20 14 0.22 23 30-60 0.43.2 1.70.02 1.1 Pot soils Sandy soil 1.62.2 1.10.10 0.41 25 8.47.8 0.238.6 Carexpeat 9.5 13 1.40.23 5.7 49 42 18 0.47 20 layer of the experimental plots were higher and the zinc concentration was lower (Table 2) than on average in Finnish cultivated soils (Erviö et al. 1990). The zinc concentration was also low in mineral pot soil and JOK soil, which were of coarser texture than other soils. The zinc con- centrations were, however, within the large range of zinc in Finnish cultivated soils. The HAAC- EDTA-extractable nickel concentration was clearly lower in sandy pot soil than in plot soils. The concentrations of HAAC-EDTA-extractable heavy metals were somewhat lower in the deep- er layer than in the plough layer, excluding the concentration of cadmium, which was very low in the deeper layer. The high concentrations of cadmium, copper, lead and nickel in the experi- mental soils were attributed to the high clay con- tent, which exceeded that in the data published by Erviö et al. (1990). The use of fertilizer con- taining cadmium probably raised the soil cad- mium content. The HAAC-EDTA-extractable lead concentration in the plough layer on the JO fields and the AR-extractable lead concentration on the NU fields decreased with distance from the road, indicating the impact of traffic. Com- pared with levels reported in many other stud- ies, the roadside lead concentration was very low (e.g. Lagerwerff and Specht 1970, Davies et al. 1979, Collins 1984). The decrease in HAAC- EDTA-extractable copper concentrations in plough layers with distance can also be explained by traffic. Deposition The annual bulk deposition of lead estimated from the data in Table 3 was of the same magni- tude and the deposition of zinc and cadmium lower than measured in southern and central Sweden in 1984—1985 (Andersson and Gustafson 1988). In this study the measured copper depo- sition was higher and the nickel deposition much higher than the levels reported by Andersson and 40 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect ofroad traffic on heavy metal concentrations ofplants Vol. 4: 35-48. Table 3. Precipitation (Free.) and bulk deposition of some elements at the experimental sites from June 1, 1987 to October 12, 1987(1987) and from May 31, 1988 to September 20, 1988 (1988). Site Free. N S P Zn Cu Pb Cd Ni mm kg ha 1 g ha 1 1987 JOI 373 3,4 3.5 0.23 25 16 24 0.20 22 JO II 375 3.5 3.5 0.16 18 11 17 0.18 28 JO 111 376 3.3 3.4 0.08 21 40 16 0.20 27 NU I 325 2.9 3.0 0.13 24 25 27 0.19 20 NU II 322 3.0 2.8 0.11 16 15 17 0.16 31 NU 111 319 3.0 2.8 0.10 20 66 15 0.22 39 JOK 335 3.0 3.1 0.14 29 7 12 0.18 17 1988 JOI 243 2.1 1.9 0.07 19 41 14 0.30 25 JO II 246 2.0 1.9 0.07 13 38 10 0.09 23 JO 111 248 1.8 1.9 0.10 9 39 7 0.23 28 JOK 243 1.8 2.0 0.07 20 33 7 0.16 21 Gustafson (1988). Hovmand et al. (1983) report- ed that the monthly bulk deposition of cadmium during the growth period in Denmark was 0.12- 0.26 g ha~', which was about the same as that found here during over four months. With the exception of copper, the bulk deposition of ele- ments was of the same magnitude at both exper- imental sites. In 1987, copper deposition was highest at 200 m from theroads. The lowest bulk deposition of heavy metals was measured on a field at Jokioinen, which can be considered a typical “clean” area in southern Finland. Traffic density is higher at Nurmijärvi than at Jokioi- nen, and thus higher lead deposition could be expected at Nurmijärvi. The relatively high lead deposition found at Jokioinen may be due to the wind, which frequently blew from the road to- wards the experimental plots. The cadmium val- ues in theair were as low on JO I, the field near- est the road, as on the “backround” field, JO 111, 200 m from the road (Fig. 3). The highest lead and cadmium concentrations (Figs 2 and 3) in the air during June and July correlated closely with the direction of the wind. Zinc deposition decreased with an increase in distance from the road. Similar findings have been reported by Albasel and Cottenie (1985) for lead and zinc and by Johnston and Harrison (1984) for cadmium, copper and lead. In the study of Johnstonand Harrison (1984), the depo- sition rate fell slowly beyond 20 m, and reached “background” levels by over 200 m, which dis- tance was taken as the background in this study, too. In both of the above studies, the traffic den- sity was much higher than in this study. The high- est lead concentration in the air found here (Fig. 2) was less than one-tenth of the lowest accept- able limit value set by WHO (1987) or, on aver- age, one-tenth of that measured in a central Lon- don park (Jensen and Laxen 1987). Metal uptake by plants In most cases, the yields did not vary much with- in the plots or from plot to plot (Table 4-7). No abnormal differences in calcium, magnesium, potassium, phosphorus or sulphur concentrations were seen between plants grown on plots and those grown in pots. Therefore, these figures are omitted from the final results. The data published by Davies et al. (1979) 41 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect ofroad traffic on heavy metal concentrations ofplants suggest that an accumulaltion of EDTA-extract- able lead of approximately 350 mg kg' 1 is nec- essary before radish will absorb sufficient lead to cause concern. This value is very much high- er than that analysed on the HAAC-EDTA ex- tracts in this study (Table 2). The lead concentration of plants was com- monly highest on the plots and in the pots clos- est to the roads (Table 4-7), where lead deposi- tions were also highest (Table 3, Fig. 2). How- ever, in wheat grain, the lead concentration was very low and did not change with distance from Fig. 2. Dry deposition of Pb measured from dust filters. Each point presents sampling for 3-4 days. The squares are joined by a line for ease of readability. Fig. 3. Dry deposition of Cd measured from dust filters. Otherwise as in Fig. 2. 42 AGRICULTURAL SCIENCE IN FINLAND Vol. 4: 35-48. Table 4. Mean dry matter yield (g/plot or pot) and heavy metal concentrations (mg/kg of dry matter) of lettuce at various distances from the roads at Nurmijärvi and Jokioinen in 1987. Nurmijärvi Jokioinen 22 m 58 m 200 m 22 m 58 m 200 m Lettuce Plots Yield 780 770 1290 1450 1590 1260 Zn 47"( l 42*(1 45*(1 35a(l 37a (l 34a(l Cu 8.0*(2 7.8a(2 9.0"(2 6.1*(2 7.7a (2 6.1*(2 Pb 0.87 a 0.45b(3 0.32b 0.58a 0.35b(3 0.32 b Cd 0.97a(3 1.12a(4 0.56b 0.77a(3 0.59ab 0.51 b(3 Ni 1.79a(4 1.54a(5 1.18b (3 2.06a(4 1.80a (4 1.43a(4 Pois Yield 21.6 a 16.5ab 15.3b 19.0“ 20.2a 21.7* Zn 32a(l 32a(l 36a ( 1 26*(1 28a (l 25*(1 Cu 4.9a(2 5.1 a(2 5.7a (2 3.8 b(2 5.0*(2 4.2 a(2 Pb 0.96a 0.57b(3 0.39b 0.65* 0.50b(3 0.36' Cd 0.54a(3 0.67a(4 0.71" 0.38a(3 0.49" 0.39(3 Ni 0.41 "(4 0.3 l a(s 0.36"(3 0.88"(4 0.49a(4 0.41(4 Means not marked with a common letter differ from each other at the 1% level of significance (Tukey's HSD, Honestly Significant Difference, test). Mean heavy metal concentration on the plots and in pots marked with the same number differ from each other at the 1 % level of significance (t-test). The fields were tested separately. the road. Ward et al. (1979) have reported anom- alous lead levels in vegetation in the downwind direction at a similar traffic density. The influ- ence of automotive emissions extends as a lead halo within 30-50 m of the road (Ward et al. 1979, Crump and Barlow 1982, Rodn'gues- Flores and Rodngues-Castellön 1982), which is about the same distance as measured here. Be- cause plants take up lead mainly from air depo- sition (e.g. Ward et al. 1979), those grown on plots and in pots received about the same lead concentrations. The highest zinc, cadmium and nickel con- centrations were recorded in lettuce (Table 4- 6). The zinc concentration of wheat grain and the nickel concentration of Italianrye grass were also high. The cadmium concentration was low in wheat and rye grass. In wheat, the zinc and copper concentrations were higher and the lead and cadmium concentrations much lower in grain than in straw. The high copper deposition at 200 m from the roads did not affect the copper con- centration of plants. The coarse pot soil was poor in zinc, copper and nickel, which probably ex- plains the higher metal concentration often meas- ured in plants grown on the plots than in those grown in pots. Plants readily accumulate atmospheric cad- mium (Hovmand et al. 1983, Naturvårdsverket 1987). Here the behaviour of cadmium differed from that of the other heavy metals. Its concen- tration was mostly higher on plots than in pots oflettuce but always higher in pots than on plots of wheat grain and, in most cases, also in the first cut of rye grass. Ho and Tai (1988) report- ed a good correlation between traffic flow and zinc, copper and cadmium concentrations in grass sampled within 3 m of the road kerb. Ward et al. (1977) showed that the relationship be- tween heavy metal concentrations in plants and traffic volume also depends on the plant species concerned. These findings together with the low zinc, copper, cadmium and nickel concentrations measured in roadside grass and soil help us to 43 AGRICULTURAL SCIENCE IN FINLAND Table 5. Mean dry matter yield (g/plot or pot) and heavy metal concentrations (mg/kg of dry matter) of spring wheat grain and straw at various distances from the roads at Nurmijärvi and Jokioinen in 1987. Nurmijärvi Jokioinen 22 m 58 m 200 m 22 m 58 m 200 m Grain Plots Yield 1700 1450 1670 2060 1580 1860 Zn 30 b 30 b 34» 33a 33* 37“(1 Cu 3.9b(l 3.9b( 1 4.9*(1 4.9“(1 4.6 a(l 5.4a(2 Pb 0.030a 0.019a 0.020“ 0.026a 0.029“ 0.016* Cd 0.009“(2 0.008“(2 0.007“(2 0.007“(2 0.008a(2 0.010“(3 Ni 0.30“(3 0.25 a(3 0.27a(3 0.32 b(3 0.41 ab(3 0.45a (4 Pots Yield 28.0“ 24.3 b 18.5b 34.5“ 34.9“ 33.6“ Zn 37“ 34“ 39“ 33“ 34“ 32“(1 Cu 2.8“(1 2.4“(1 2.3“(1 2.9“(1 2.9“(1 2.5“(2 Pb 0.037“ 0.019“ 0.019“ 0.023“ 0.018“ 0.015" Cd 0.018“(2 0.017“(2 0.029“(2 0.021“(2 0.019“(2 0.019“(3 Ni 0.070“(3 0.060“(3 0.068“(3 0.052“(3 0.064“(3 0.050“(4 Straw Plots Yield 3830 4020 4600 6630 5590 6750 Zn 9.3“b 7.6 b 10.6“ 8.5“ 8.7“ 11.6(1 Cu 1.6* 1.3b 1.5“b 1.6“ 1.4“ 1.5“ Pb 0.88“(1 0.34b 0.28b( 1 0.51“ 0.33" 0.14 b (2 Cd 0.061“ 0.040“b( 1 0.034b(2 0.067“ 0.056“(I 0.055“ Ni 0.102“ 0.078“ 0.044“ 0,080“ 0.072“ 0.044“ Pots Yield 95.8“ 93.2“ 63.3b 100“ 118“ 106“ Zn 10.4“b 8.1 b 11.6“ 8.9“ 9.2“ 8.9“(l Cu 1.5“ 1.2“ 1.5“ 1.4“ 1.3“ 1.2“ Pb 1.10“(1 0.33b 0.39b( I 0,44“ 0.41“ 0.21 b(2 Cd 0.092b 0.07 l b(l 0.117"(2 0.093“ 0.091"(I 0.080“ Ni 0.082“ 0.030“ 0.100“ 0.086“ 0.090“ 0.060“ Statistical tests as in Table 4. Grain and straw were tested separately. understand the slight discrepancies in the results of this study. In 1988, the heavy metal concentrations in plants were similar to those in the yields in 1987 (Table 7), which confirmed the results measured on the NU and JO fields in 1987. The lead con- centration was often highest at the experimental site nearest the road, although not as clearly as in 1987. Conclusion This study shows that the zinc, copper, lead, cad- mium and nickel concentrations along roadsides are low at current traffic densities. The influence of lead emissions extended within 50 m of the road. The anomalous lead and cadmium concen- trations in dry deposition were attributed to wind 44 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect of road traffic on heavy metal concentrations ofplants Vol. 4: 35—48. Table 6. Mean dry matter yield (g/plot or pot) and heavy metal concentrations (mg/kg of dry matter) of rye grass at various distances from the roads at Nurmijärvi and Jokioinen in 1987. Nurmijärvi Jokioinen 22 m 58 m 200 m 22 m 58 m 200 m I cut Plots Yield 2120 2410 1790 2270 2170 2420 Zn 22* 18b 19*b(l 20* 21* 22* Cu 5.8* 5.2“ 5.5* 6.5“(1 6.3*(1 6.4“(1 Pb 0.55* 0.27b(l 0.17* 0.63* 0.35 b 0.24 b Cd 0.038*(I 0.039*(2 0.023*(2 0.019b(2 0.059“ 0.039* b Ni 1.19*(2 0.97b(3 0.98b(3 1.27b(3 1.57‘(2 1.41*b(2 Pots Yield 77.0* 74.7* 68.7* 91.8* 87.9* 88.2* Zn 22* 22* 25“(1 22" 22* 20* Cu 5.5* 5.1* 5.5* 5.7*(1 5.4*(1 5,0*(1 Pb 0.49“ 0.24b(l 0.18b 0.65* 0.45* 0.24* Cd 0.070b( 1 0.068b(2 0.117*(2 0.036b(2 0.064* 0.057* b Ni 0.23*(2 0.17*(3 0.20*(3 0.25*(3 0.30*(2 0,25*(2 II Cut Plots Yield 3620 3840 3900 3130 3550 3360 Zn 18“ 16a 17" 15“ I4"(l 16" Cu 6.5’(1 6.0*(1 6.6"( 1 6.1 *( 1 5.6"(2 5.8"(1 Pb 1.25“ 0.86b 0.56" 0.92“ 0.54b 0.50b Cd 0.034“ 0.041” 0.026"(2 0.032“ 0.015“ 0.029“ Ni 1.27“(2 1.16“(2 1.11“(3 0.97 b(2 1.30*(3 1.18’(2 Pots Yield 71.8" 70.0" 65.8" 67.0“ 78,2“ 73.2’ Zn 17“ 17“ 16" 16" 16“(1 15“ Cu 4.7“(1 4.4*(1 4.1*(1 4.7’(l 4.0"(2 3.9’(1 Pb 1.17“ 0.78 b 0.54" 0.84“ 0.54b 0.44" Cd 0.033’ 0.038’ 0.044’(2 0.027’ 0.023’ 0.026’ Ni 0.32*(2 0.26*(2 0.27’(3 0.21*(2 0.25“(3 0.22*(2 Statistical tests as in Table 4. The cuts were tested separately. direction. The heavy metal concentrations var- ied between different plant species and also be- tween different plant parts. These results are consistent with those published by Yläranta and Sillanpää (1984), and indicate the complexity and difficulty of interpreting the results of plant analyses when estimating the heavy metal sta- tus of respective soils and vice versa. The re- sults obtained in the study of Sillanpää et al. (1988), in which the lead concentrations of dif- ferent plant species grown side by side at nine locations in Finland, support the contention that most of the lead in crops is airborne. This find- ing is confirmed here. 45 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect of road traffic on heavy metal concentrations ofplants Table 7. Mean dry matter yield (g/plot or pot) and lead concentrations (mg/kg of dry matter) of lettuce, spring wheat grain and straw, and rye grass at various distances from the road at Jokioinen (JO) in 1988.Means not marked with a common letter differ from each other at the 1% level of significance (Tukey’s HSD test). Lead concentrations of different plants grown on the plots and in pots marked with the same number differ from each other at the 1% level of significance (t-test). Jokioinen Reference 22 m 58 m 200 m area Lettuce Plots Yield 1280 1070 1090 840 Pb 0.58“ 0.54“ 0.53“ 0.67*(1 Pots Yield 51.1“ 38.3“b 45.7“ 24.5b Pb 0.66“ 0.46b 0.42 cb 0.25 c(l Wheat grain Plots Yield 1920 2820 2760 2110 Pb 0.033“b 0.020b 0.047“(2 0.026“ b Pots Yield 21.0 b 32.4“ 15.0b 13,4b Pb 0.026“ 0.015“ 0.018b(2 0.031" Wheat straw Plots Yield 3170 2860 2580 2120 Pb 0.67“ 0.49“b 0.30b(3 0,34 b (4 Pots Yield 26.6“ 28.1“ 30.0“ 26.5“ Pb 0.61“ 0.33 b 0.15 b(3 0.18 b (4 Jokioinen Reference 22 m 58 m 200 m area Rye grass I cut Plots Yield 2420 2500 2130 1780 Pb 0.55a (5 0.45a 0.24b(6 0.22b Pots Yield 74.0» 79.2» 66.2 ,b 49.3 b Pb 0.91 »(5 0.54b 0.33c (6 0.29c II Cut Plots Yield 2740 2820 2760 2940 Pb 1.09» 0.57b O-SS* 0.34c Pots Yield 35.9ab 37.2a 41.2 a 28.3b Pb 1.09“ 0.66b 0.44 b 0.4 lb 111 Cut Plots Yield 2050 1990 2370 2680 Pb 0.66» 0.56a 0.26b 0.30b (7 Pots Yield 20.7ab 5.6‘ 25.5» 19.0b Pb 0.86» 0.6l b 0.29‘ 0.36c(7 References Albasel, N. & Cottenie, A. 1985. 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Micronutrient con- tents of different plant species grown side by side. An- nales Agriculturae Fenniae 23: 158-170. 47 AGRICULTURAL SCIENCE IN FINLAND Yläranta, T: Effect ofroad traffic on heavy metal concentrations ofplants SELOSTUS Maantieliikenteen vaikutus viljelykasvien raskasmetallipitoisuuteen Toivo Yläranta Maatalouden tutkimuskeskus Sinkin, kuparin, lyijyn, kadmiumin ja nikkelin ker- tymistä lehtisalaattiin, vehnän jyviin ja olkiin sekä italianraiheinään tutkittiin vuonna 1987 Valtatie 3:n varrella Nurmijärvellä ja Valtatie 2:n varrella Joki- oisissa 22, 58 ja 200 m:n etäisyydellä teiden reuna- viivasta. Koe uusittiin Jokioisissa vuonna 1988. Koepaikoille 1,8 m:n korkeuteen asetetuilla ke- räimillä kerättiin vuosina 1987 ja 1988 märkälas- keuma ja se osa kuivalaskeumasta, joka vapaasti laskeutuu ilmasta keräimeen. Tämän “kokonaislas- keuman” ohella kerättiin ilman kuivalaskeuma vuon- na 1988 pölynkeräimillä suodattimille 22 ja 200 m:n etäisyydellä tiestä. Kuivalaskeumasta mitattiin lyijy- jä kadmiumpitoisuus. Lyijyn kokonaislaskeuma oli 22 m:n etäisyydellä tiestä 50 % suurempi ja kuiva- laskeumakin selvästi suurempi etäisimpään mittaus- pisteeseen verrattuna. Myös sinkin kokonaislaskeuma pieneni hieman siirryttäessä tietä lähimmästä mit- tauspaikasta etäisimpään mittauspaikkaan. Kadmi- umin kokonais- ja kuivalaskeuma olivat pieniä kaikilla mittauspaikoilla. Lyijyn jakadmiumin kuiva- laskeuma oli suurin silloin, kun tuuli puhalsi tieltä keräimiin päin. Kasvien raskasmetallipitoisuudet olivat erisuuria eri kasveissa, mutta pitoisuuserot koepaikkojen vä- lillä olivat pieniä. Suurimmat sinkki-, kadmium- ja nikkelipitoisuudet olivat lehtisalaatissa. Myös vehnän jyvien sinkkipitoisuudet ja italianraiheinän nikkeli- pitoisuudet olivat suuria. Vehnän jyvien ja olkien sekä italianraiheinän kadmiumpitoisuudet olivat pieniä. Vehnän jyvien sinkki- ja kuparipitoisuudet olivat suu- rempia ja lyijy- ja kadmiumpitoisuudet paljon pie- nempiä kuin olkien pitoisuudet. Pääosan sisältämästään lyijystä kasvit ottivat las- keumasta. Tien reunasta 22 m:n päässä oli kasvien lyijypitoisuus 1,5-3 -kertainen verrattuna 200 m:n etäisyydellä tiestä olleeseen kasvupaikkaan. Etäi- simmän kasvupaikan kasvien lyijypitoisuus ja lyijy- laskeumakin viittasivat tilanteeseen, joka oli “puh- taalla” vertailukoepaikalla Jokioisissa. Tutkituista raskasmetalleista ainoastaan lyijyllä on ollut merkitystä viljelykasvien “likaajana” maan- teiden varsilla. Likaaminen on ulottunut noin 50 m:n etäisyydelle tiestä. Pääosa laskeumissa mitatusta lyi- jystä on ollut peräisin bensiinistä. Koska lyijyä on mitattu myös etäällä maantiestä, on suuri osa liiken- teen lyijypäästöistä kulkeutunut todennäköisesti kau- as tiestä. 48 AGRICULTURAL SCIENCE IN FINLAND