TIME, SUNLIGHT, AND THE FATE OF BIOTREATED KRAFT MILL ORGANOCHLORINES(AOX) IN NATURE

A system of gas- and light-permeable sealed sample bags was employed t o monitor the fate and persistence of the color and organochlorines (A OX) exiting the secondary treatment systems of three modern pulp and p aper kraft mills. Placed in a remote lake at various depths, the bags of effluent showed that the ''stable'' biotreated AOX from elemental c hlorine-free bleaching was largely but not completely mineralized in 4 months, largely by sunlight-dependent processes. Mill AOX and color w as partially protected from photomineralization by natural organic mat ter (NOM) in the water. Effluent chromophores were more rapidly and co mpletely degraded by light than AOX, and neither AOX nor color were ve ry susceptible to biological degradation. The biotreated effluents, ev en when undiluted, were not acutely toxic and over time gave rise to d iverse, flourishing microalgal, protozoan, and metazoan communities in the sealed bags. Thus these concentrated effluents apparently had no acute or chronic toxicity for a diverse assemblage of aquatic organism s over a 4-month period. Copyright (C) 1996 Elsevier Science Ltd