Kraft mill residues effects on Monterey pine growth and soil microbial activity

The production of bleached Kraft pulp generates inorganic and organic residues that are usually deposited on the soil surface or landfilled. Studies conducted to address the impact of these wastes on the environment are scarce. In this work, Monterey pine (Pinus radiata D. Don), an important tree for pulping, was evaluated for germination and development under greenhouse conditions in forest soils exposed to solid residues of the cellulose industry using the Kraft process. Soils exposed to 10 to 60% ashes, 10 to 70% fly ashes, or 10 to 30% dregs allowed substantial seed germination and seedling growth. In contrast, soils exposed to low proportions of brown rejects, grits, or a mixture of all these residues were detrimental for germination, plant growth, or both. The strongest negative effect (no germination) was observed with as low as 10% grits. The changes in pH and/or water content caused by solid wastes did not correlate with detrimental effects observed in various soil-residue combinations. No significant changes in the microbial community of soils exposed to these solid residues were observed by determination of culturable counts, or by terminal-restriction fragment length polymorphism analysis of the microbial community DNA. The presence of organic residues did not affect the ability of the soil microbial community to remove typical pulp bleaching chloroaromatics. However, inorganic wastes strongly decreased the removal of such compounds.