ABSTRACT
The deposit-feeding amphipod Monoporeia affinis was exposed in soft bottom microcosms to fractionated organic extracts of bottom sediments collected outside a pulp and paper mill. Changes in the biological effects of sediment extracts were tested before and after altering the bleaching process at the mill, i.e., a change from chlorine gas to elemental chlorine free (ECF) bleaching in combination with substantial decreases in total wastewater and COD discharges. Sediment samples representing material deposited before (10–12 cm) and after (0–2 cm) this event, as well as sediments (0–2 cm) from the central Bothnian Sea, were Soxhlet extracted with toluene. The extracts were fractionated by HPLC into three fractions containing aliphatic/monoaromatic, diaromatic and polyaromatic compounds. Control sediments were dosed with the extracts and placed in soft bottom microcosm test systems. After an exposure period of 5 months, reproduction success, fecundity, embryonic development and different types of embryonic malformation were studied in amphipods. All fractions of the sediment from the pulp mill were toxic, except the polyaromatic fraction from surface sediment (0–2 cm) and the aliphatic/monoaromatic fraction from 10–12 cm depth. However, the effects of the fractions were lower than for corresponding non-fractionated sediment extracts in both depths. The polyaromatic fraction from the 10–12 cm depth exceeded the surface sediment fraction and the others in toxicity, indicating improved conditions as a result of the reduced discharge from the mill.
