The effects of occupational exposure to hydrocarbons on some immune parameters of workers of the phenol division of a petrochemical plant - Zeman, Krzysztof; Tchórzewski, Henryk; Baj, Zbigniew; Nowak, Zofia; Majewska, Ewa; Pokoca, Lech; Kocur, Eugeniusz; Kantorski, Jerzy (Nofer Institute of Occupational Medicine)