▁O bu asi ▁was ▁over ▁ 1 0 – 3 8 ▁times ▁the ▁maximum ▁amount ▁that ▁is ▁allow able ▁by ▁law . ▁The ▁two ▁main ▁sources ▁of ▁the ▁cont am ination ▁is ▁the ▁ar sen ic ▁pow der ▁that ▁flows ▁out ▁from ▁the ▁mill s ▁and ▁the ▁extensive ▁amount ▁of ▁run - off ▁water ▁that ▁is ▁dis posed ▁of ▁through ▁d ams . ▁" Th us ▁in ▁the ▁processing ▁of ▁the ▁ore ▁for ▁gold , ▁the ▁dust ▁may ▁contain ▁particles ▁of ▁the ▁ore , ▁fer ric ▁ox ide , ▁ox ides ▁of ▁ar sen ic ▁and ▁sul ph ur ". ▁The ▁dust ▁will ▁then ▁get ▁carried ▁into ▁the ▁atmosphere ▁and ▁sett le ▁on ▁the ▁soil , ▁humans , ▁and ▁rivers . ▁In ▁O bu asi , ▁they ▁receive ▁a ▁high ▁annual ▁ra inf all ▁due ▁to ▁the ▁tropical ▁rain for est ▁that ▁surr ounds ▁it ▁( S med ley , 1 9 9 6 , 4 6 4 ). ▁During ▁precip itation ▁or ▁ra inf all , ▁the ▁dust ▁" may ▁be ▁ox id ized ▁to ▁the ▁tri ox ide ▁by ▁the ▁air ▁and ▁be ▁converted ▁to ▁the ▁sul ph ate ▁in ▁de w ▁and ▁rain water ". ▁The ▁soil ▁is ▁the ▁main ▁target ▁of ▁cont am ination ▁because ▁the ▁soil ▁is ▁cont amin ated ▁and ▁whatever ▁veget ation ▁grows ▁and ▁dec ays ▁goes ▁right ▁back ▁in ▁the ▁soil ▁which ▁results ▁in ▁the ▁cont am ination ▁of ▁the ▁ground water . ▁However , ▁the ▁ground water ▁is ▁not ▁as ▁poll uted ▁as ▁the