A method and device are presented for affecting at least one chemical or mechanical property of a target site (109). A stream of liquid towards a contact with the target site (109) is provided with a predetermined flow rate. Also provided is UV-radiation (103) having predetermined parameters in terms of power, wavelength, duty cycle and repetition rate. The UV-radiation (103) is directed within the stream of liquid (101) along a trajectory of the stream. The stream carrying the UV radiation is maintained in contact with the target site for a time period and under conditions sufficient for affecting the at least one chemical or mechanical property.