Mezue ahịrịokwu na-esonụ: Njikọ nke mmiri ọkụ na mmetọ bụ ikike ya ịgbasa ngwa ngwa ma ọ bụrụ na ejighị ya mee ihe nke ọma mgbe ejiri ya maka ọkụ ọkụ; mmiri ọkụ na-agbapụ na-abụkarị onye na-emejọ ma ọ bụ onye na-enye aka na ọtụtụ mmetọ mmetọ kemịkal (lee Mmiri mmetọ). Ihe
Dịka ọmụmaatụ, nsị kemịkalụ Sandoz nke 1986, mere ka osimiri Rhine na-acha uhie uhie site na mmetọ ma metụta ọtụtụ n'ime anụ ọhịa n'ihi njigide na-ezighị ezi nke mmiri ọkụ ejiri mee ihe n'ịgwọ ọkụ ụlọ nkwakọba ihe agrochemical, na-ahapụ tọn 30 nke kemịkal na-egbu egbu n'ime osimiri ahụ.