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Increased ethoxyresorufin-O-deethylase (EROD) activity is a sensitive biomarker of exposure to the chemicals which activate the aryl hydrocarbon receptor (AhR) and induce the cytochrome P450 system, such as many polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs). Pulp bleaching was one of the main sources of PCDDs and PCDFs until elemental chlorine free (ECF) and total chlorine free bleaching processes since 1990s have remarkably decreased but not completely eliminate discharges of these chemicals. In addition, historically contaminated sediments may act as a source of these persistent contaminants. In this study, the contamination history and recovery of a watercourse heavily loaded by the chemical wood industry were studied by analyzing PCDDs, PCDFs and PCBs from vertical sediment samples and by measuring hepatic EROD activity from rainbow trout intraperitoneally dosed with the sediment extracts. No PCDDs or PCDFs were found above the chromatographic limit of detection from the study area and only small amounts of PCB congeners 101, 138, 153, and 180 were present. No increased EROD activity was observed in fish indicating the absence of any AhR-activating compounds in the surface sediment, to about 15 cm depth, representing about the last 20 years when kraft pulping and ECF bleaching with activated wastewater treatment have been used. It can be concluded that nowadays organochlorines and other AhR-ligands do not harm the previously heavily polluted watercourse.

The wastewater treatment plant of an elemental chlorine free bleaching kraft pulp mill located in eastern Finland was sampled in order to study the fate of wood extractives and the toxicity to luminescence bacteria (Vibrio fischeri) in different parts of the plant. Resin acids and sterols were analyzed from water, particles and sludge samples during three different runs. Waters before biotreatment and primary sludge were found to be toxic; but in the activated sludge treatment toxicity was removed. During wastewater treatment, concentrations of wood extractives were reduced over 97%. In activated sludge treatment, over 94% of the resin acids and over 41% of the sterols were degraded or transformed to other compounds. Furthermore, in general, less than 5% of the resin acids and over 31% of the sterols were removed in biosludge to the sludge thickener. Most of the extractives were discharged attached to particles. Although some disturbing factors increased the load of wood extractives during samplings, these factors did not affect the operational efficiency of the secondary treatment system.

The concentration of retene, a di-alkyl substituted PAH derived microbially and thermally from dehydroabietic acid, eight resin acids and their derivatives were analysed from sedimenting particles collected from five lake sites receiving pulp and paper mill effluents and from two reference sites. At five of the sites, samples were collected prior and after a conventional aerated lagoon wastewater treatment system of the mill was modernized with an activated sludge plant, and elemental chlorine free bleaching (ECF) had replaced chlorine bleaching. The highest level of retene was 30.0–53.8 μ g/g dry weight (d.w.), observed 3 km downstream from the mill. Nine kilometers downstream from the mill the concentration of retene was still 8.7–17.4 μ g/g d.w., distinctly exceeding that of the upstream reference (0.2–4.4 μ g/g d.w). The highest concentration of resin acids was 1474 μ g/g d.w., the most abundant resin acid being dehydroabietic acid. The concentrations of retene and resin acids showed a distance related decrease downstream to a mill. The technology changes at the pulp and paper mill decreased both the sedimentation rate and the concentration of resin acids and retene in sedimenting particles. Presence of other resin derived neutral compounds (dehydroabietin, tetrahydroretene and fichtelite) in sedimenting particles was also revealed.

A preliminary investigation on the contribution and origin of organic halogens (measured as AOX) in sludges out of pulp and paper production is described. Size exclusion chromatography (SEC) and indirect enzyme-tests (cellulase) have shown remarkable differences in AOX-substances between various fractions of paper sludges. In sludges from factories with 100% pulp usage (pulp sludges) chlorinated polymers from the pulp bleaching with chlorine were identified as main source. In sludges from companies with 100% waste paper usage (waste paper sludges) strong indication has been presented that the main AOX-sources are contaminations in printing inks and smaller fragments of chlorinated wood polymers, especially lignin. For the improvement of paper sludge disposal in Europe (especially Germany) it is important to decrease the AOX-contents by substitution of AOX-containing printing inks and by transforming the traditional chlorine bleaching of pulp to elemental chlorine free (ECF) or total chlorine free (TCF) processes.