▁▁ ▁Some ▁Cl - PA H s ▁have ▁struct ural ▁similar ities ▁to ▁dio x ins , ▁they ▁are ▁sus pected ▁of ▁having ▁similar ▁to xic ities . ▁These ▁types ▁of ▁comp ounds ▁are ▁known ▁to ▁be ▁car cin ogen ic , ▁mut agen ic , ▁and ▁ter at ogen ic . ▁To xic ological ▁studies ▁have ▁shown ▁that ▁some ▁Cl - PA H s ▁possess ▁greater ▁mut agen icity , ▁ar yl - h yd or car bon ▁re ceptor ▁activity , ▁and ▁dio x in - like ▁to x icity ▁than ▁the ▁corresponding ▁parent ▁PA H s . ▁ ▁The ▁relative ▁pot ency ▁of ▁three ▁ring ▁Cl - PA H s ▁was ▁found ▁to ▁increase ▁with ▁increasing ▁degree ▁of ▁ch lor ination ▁as ▁well ▁as ▁with ▁increasing ▁degree ▁of ▁ch lor ination . ▁However , ▁the ▁relative ▁pot encies ▁of ▁the ▁most ▁to xic ▁Cl - PA H s ▁ass essed ▁up ▁to ▁now ▁have ▁been ▁found ▁to ▁be ▁ 1 0 0 , 0 0 0 - fold ▁lower ▁than ▁the ▁relative ▁pot ency ▁of ▁ 2 , 3 , 7 , 8 - t et rach lor od iben zo - p - d io x in ▁( T CD D ). ▁Even ▁though ▁Cl - PA H s ▁aren ’ t ▁as ▁to xic ▁as ▁T CD D , ▁it ▁has ▁been ▁determined ▁using ▁recom bin ant ▁b acter ial ▁cells ▁that ▁the ▁to xic ities ▁of ▁expos ure ▁to ▁Cl - PA H s ▁based ▁on ▁Ah