The maintenance of safe-drivingconditions in snow and ice-affected areas in thewintertime includes the use of sodium chloride (NaCl)as de-icing salts. In this study, the impact of NaClon soil-colloid mobilisation and exchangeablebase-cation leaching has been evaluated. The chemistryof groundwater samples below an infiltration trenchfor highway runoff and leachate from column studiessuggested that soil-colloid mobilisation had occurred,as the exchangeable sodium (Na) concentration and theelectrical conductivity (EC) in the groundwater/columnleachate reached the threshold values for colloiddispersion. Generally, samples with no dispersionproblems had high Na and calcium (Ca) concentrations,suggesting that the initial effect of the de-icingsalt was to stabilise the colloids. In the columnstudy there was a good agreement between the degree ofcolloid dipersion problems and lead (Pb) concentrationwhen the pH value was above 7.0. Significant negativecorrelations between Na/CEC (cation exchange capacity)and Ca/CEC in roadside soils from three sitesindicated that Na preferentially displaces Ca from theexchange sites. However, the groundwater dataindicated that Na ions also displace potassium (K) andmagnesium (Mg). A positive effect of NaCl seen at onesite was an increase in the K concentration, which ishighly likely an effect of Na ions displacing fixed Kbetween the layers of 2:1 type clay minerals. In soilslacking these types of clay minerals, severe Kshortage may result from a high plant demand combinedwith the low K concentration in the readily availablefractions in the original soil and a highsusceptibility to leaching. The most significantimpact on soil exchange processes was found to occurwithin 6 m from the road.

Laboratory and field experiments werecarried out with 2,4-D herbicide(2,4-Dichlorophenoxyacetic acid) to evaluate itstransformation and migration in the coastal waterprotection zones of the Oka river, Russia. In thefirst laboratory experiment, the transformation of2,4-D was studied in various soil samples from coastalslopes (1–0°) of 480 m length soil-geochemicalcatena on the right side of the Oka river incomparison with watershed and floodplain soils. Thetransformation of 2,4-D was the lowest in soil sampleswith minimal pH values and was independent of eitherslope values or vicinity to the Oka river channel.Using indirect estimates, the surface runoff potentialwas calculated for this herbicide. In the second fieldexperiment, the vertical migration and transformationof 2,4-D was carried out in soddy sand soil (EutricArenosol) placed in the left side of the Oka river(0-100 cm) under `soft' (40 mm 2 hr⁻¹) and `hard'(40 mm 15 min⁻¹) irrigation regimes. Furthermore, thetransformation of this herbicide was studied in 0–20and 40–50 cm soil layers under various temperature andmoisture regimes. After 1 day of irrigation, the mainherbicide quantity was found in the 0–30 cm layerunder both irrigation regimes. The transformation ofthe herbicide was faster in the surface, 0–20 cmlayer, than in the deeper, 40–50 cm layer.