A numerical one-dimensional radial time-dependent model of particle and energy transport in tokamak plasmas taking the interaction of background and impurity particles through the radiation losses of energy and ion dilution is developed. Detachment in ohmic discharges caused by an increase in the electron density is modelled and the effect of particle and energy transport on detachment conditions is studied. Investigation of dynamic changes in plasma parameters during detachment provoked by an increase in impurity influx is performed. The effect of the nature of heat source on the stabilization of the radiating layer is elucidated. The influence of neo-classical transport and charge-exchange with hydrogen neutrals on the impurity behaviour in 'attached' and 'detached' plasmas is discussed.