R ▁activity ▁were ▁approximately ▁ 3 0 - 5 0 ▁times ▁higher ▁than ▁that ▁of ▁dio x ins . ▁Cl - PA H s ▁demonstrate ▁a ▁high ▁enough ▁to x icity ▁to ▁be ▁a ▁potential ▁health ▁risk ▁to ▁human ▁populations ▁that ▁come ▁into ▁contact ▁with ▁them . ▁ ▁DNA ▁interaction ▁▁ ▁One ▁of ▁the ▁well - est ab lished ▁mechan isms ▁by ▁which ▁ch lor in ated ▁poly cyc lic ▁a rom atic ▁hydro car b ons ▁can ▁ex ert ▁their ▁to xic ▁effects ▁is ▁via ▁the ▁function ▁of ▁the ▁ar yl ▁hydro car bon ▁re ceptor ▁( Ah R ). ▁The ▁Ah R - medi ated ▁activities ▁of ▁Cl - PA H s ▁have ▁been ▁determined ▁by ▁using ▁ye ast ▁ass ay ▁systems . ▁A ry l ▁H ydro car bon ▁Re ceptor ▁( Ah R ) ▁is ▁a ▁c yt os ol ic , ▁lig and - activ ated ▁trans cription ▁re ceptor . ▁Cl - PA H s ▁have ▁the ▁ability ▁to ▁bind ▁to ▁and ▁activ ate ▁the ▁Ah R . ▁The ▁bi ological ▁path way ▁involves ▁trans location ▁of ▁the ▁activ ated ▁Ah R ▁to ▁the ▁nucle us . ▁In ▁the ▁nucle us , ▁the ▁Ah R ▁bind s ▁with ▁the ▁Ah R ▁nuclear ▁transl ator ▁protein ▁to ▁form ▁a ▁heter od imer . ▁This ▁process ▁leads ▁to ▁trans cription al ▁mod ulation ▁of ▁gen es , ▁causing ▁ad verse ▁changes ▁in ▁cell ular ▁processes ▁and ▁function . ▁ ▁Several ▁Cl - PA H s ▁have ▁been ▁determined ▁to