The sister chromatid exchange test as an indicator of marine pollution: some factors affecting SCE frequencies in Mytilus galloprovincialis

The sister chromatid exchange (SCE) test is a widely used method to detect chemically induced genetic damage. This method has been applied in some aquatic species to monitor genetic pollutants in estuarine and marine environments. Dose response to 5-bromodeoxyuridine (BrdU) was investigated in the mussel Mytilus gallopror~incialis Lmk. Experimental assays were carried out by incorporating 4 , 10, 20 and 40 pg ml-l BrdU in asynchronously growing mussel gill cell populations. SCE frequency was dose dependent both for mussel cells labelled with BrdU for a first round of replication followed by a second round without BrdU (24 + 3 6 h), and for mussel cells labelled with BrdU for 2 consecutive rounds of replication (60 h) . For every dose assayed, s~gnificant differences in SCE frequencies were also found between these 2 kinds of BrdU treatments. The relationship between the duration of the BrdU treatment and the frequency of SCEs was also Investigated in M. galloprovincial~s. We tested the effect of in vivo BrdU incorporation for either the flrst cell cycle, or the first and second cell cycles in mussel gill cells. This paper shows that SCE frequencies remain constant for the different BrdU exposures (12+36, 12+48, 24+24, 24+36 and 36+24 h) assayed to obtain first cell cycle labell~ng, but a striking increase was noted in BrdU treatments (48, 60. 72, 84 and 96 h) for 2 consecutive cycles of labelling. A monthly study of SCE frequencies occurring in 2 natural populations from NW Spain was also performed during 1993. Significant differences in the frequency of SCE were detected both between populations and among months in the mussel populations. In most of the cases, noticeable interindividual variations in SCE frequencies were detected in mussels exposed to the same BrdU conditions.