Comp. Biochem. Physiol. Vol. 71C, pp. 21 to 25~ 1982 0306-4492/82/010021-05g03.00/0 Printed in Great Britain. All rights reserved Copyright © 1982 Pergamon Press Ltd EFFECTS OF AROMATIC HYDROCARBONS ON THE METABOLISM OF THE DIGESTIVE GLAND OF THE MUSSEL MYTILUS EDULIS L. A. VIARENGO 1 and M. N. MOORE 2 llstituto di Fisiologia Generale, Universit:~ di Genova, Palazzo delle Scienze, Corso Europe, 16132 Genova, Italia and 2Institute for Marine Environmental Research, Plymouth, England (Received 8 May 1981) Abstract--1. The results presented in this paper show that the exposure of mussels to a sublethal concentration of oil-derived aromatic hydrocarbons (30~g 1-1) for a period of 4 months significantly decreases the protein level in the digestive gland of the animals (- 17~o). 2. The activity of the nuclear RNA polymerase I and II is also significantly decreased in the digestive gland of hydrocarbon-exposed mussels (- 64~o and -18~o, respectively). 3. The RNAase(s) activity present in the nuclei from the digestive gland cells increases following the exposure of the mussels to aromatic hydrocarbons. This effect is particularly evident at high ionic strength [200 mM (NH4)2SO4]. 4. The analysis of some characteristics of the nuclear RNAase(s) (most of which is soluble and shows a maximum of activity at pH 4-5) could indicate that part of this hydrolytic enzyme may have a lysosomal origin. 5. This fact appears to be in agreement with the finding that in the mussels exposed for 4 months to aromatic hydrocarbons the lysosomal stability decreases drastically and the total content of lysosomal enzymes is significantly increased (+ 42.4~o). INTRODUCTION It has long been known that aromatic hydrocarbons, when present in seawater at high concentrations, may prove toxic even to animals such as mussels, which are usually considered particularly tolerant to the presence of pollutants in seawater (Eisler, 1975; Roberts, 1976). The high petroleum concentrations often utilized by researchers in laboratory experi- ments are only occasionally found in seawater (Bern- hard, 1975), but the continuous increase of hydro- carbon pollution (particularly in coastal and estuarine areas) has led to a need to investigate the effects that sublethal pollutant concentrations exert on the metabolism of mussels. The mussel has been chosen for these experiments because it is a sedentary, filter-feeding animal, able to accumulate within its tissues many of the pollutants present in seawater (Pringle, 1968; Sprague, 1971; Fossato, 1974; Phillips, 1976) and for these reasons it has often been utilized as a biological indicator in monitoring programs (Goldberg, 1978). In addition, it has recently been proposed to use mussels to evaluate the biological effects that the accumulation of differ- ent pollutants may exert on the physiology and metabolism of the animal, in an effort to quantify the biological impact of the pollutants (Bayne, 1979). The present investigation was undertaken to study the effects that sublethal oil-derived aromatic hydro- carbon concentrations, comparable to those found in polluted areas, may cause on the metabolism of the digestive gland of mussels. Studies have been carried out on the effect that the exposure of the mussels to aromatic hydrocarbons may exert, either on the pro- tein content or on the nuclear RNA synthesis and degradation. In addition, the effects that treatment with aromatic hydrocarbon produces on the highly developed lysosomal-vacuolar system in the digestive cells of mussels have been investigated. MATERIALS AND METHODS Experimental treatment of mussels with hydrocarbons Mussels (Mytilus edulis U), 50-60 mm in shell length, were collected from the estuary of the River Erme (Devon) and held at the seasonal ambient temperature in a system of recirculating seawater. All mussels were fed an algal diet of Phaedactylum tricornutum and Isochrysis oalbana at a concentration of 4000-6000 cells ml- 1. Mussels were continuously exposed in a flow-through system to low concentration of the water accommodated fraction (WAF) of North Sea Crude Oil (Moore et al., 1980a). Experiments were performed from October 1978 to April 1979, at hydrocarbons concentration of about 30#g1-1 (+4.5 SE). A stock of water accommodated hydrocarbon (4.2 mg 1-1) was prepared daily, by gently mixing 20 I. of seawater and 250 ml of crude oil on a magnetic stirrer for a period of 18 hr and then leaving undisturbed for a further 6 hr. The stock WAF was pumped (13 ml min 1) into the stream of inflowing seawater before entering the tank con- taining the experimental animals. The required exposure concentration was therefore determined by the flow rate of incoming seawater. Under these experimental conditions the hydrocarbon levels in the total seawater system were maintained at background concentrations by means of aer- ation and filtration. Control animals were held in a separ- ate system of recirculating seawater. The hydrocarbon concentrations in the stock, experi- mental and control tanks were monitored twice a week. Following extraction into hexane, either by means of shak- ing or steam distillation, the hydrocarbons were measured 21