PARENT SESSION
16 - Oil Pollution & Biodegradation
8:00 AM to 6:30 PM, Monday, 13 May 2002
Exhibition Area

(16-32) Measurement of degradation time for Zinc pyrithione and Copper pyrithione using Leucine incorporation Technique.

Maraldo, Kristine^*,1,2, Dahllöf, Ingela², ¹ University of Aarhus, Aarhus, Denmark² National Evironmental Research Institute, NERI, Roskilde, Denmark

ABSTRACT- The degradability of the two new antifouling biocides: Zinc pyrithione (ZPT) and Copper pyrithione (CPT) in seawater was examined. The method used in this study is a modified version of a method described by Callow and Finlay (1995), which does not discriminate between toxicity of ZPT and CPT and their potentially toxic breakdown products. This study is therefore an examination of the total degradation of ZPT and CPT and their potential toxic breakdown products. The disappearance of each compound was monitored over 5 days using a bioassay with natural assemblages of coastal marine bacteria from Roskilde Fjord, Denmark. The inhibition of leucine incorporation in marine bacteria was measured as the ecotoxicological end-point. Leucine incorporation reflects the bacterial protein synthesis and indirectly bacterial growth. To investigate photo-degradation, bacteria were exposed to ZPT- and CPT diluted in sterile seawater. The dilutions were either exposed to sunlight or kept in darkness. Bio-degradation of the compounds was examined both in solutions exposed to light and to solutions kept in darkness. For solutions exposed to light, ZPT and CPT were diluted in seawater that was either filtered through a 100 m filter (total bio-degradation) or a 2 m filter (microbial degradation). The dark solutions were only diluted in 100 m-filtered seawater. Half time for ZPT was estimated to (8.34 ± 0.9 min) and CPT (7.12 ± 0.21min) in sterile seawater exposed to sunlight. The results did not show any significant difference between total- and microbial degradation when compared to photo-degradation. Bio-degradation without influence of sunlight was significantly slower. Therefore we can conclude that photo-degradation must be the main degradation pathway of both biocides.

Key words: Biodegradation, Zinc pyrithione, Copper pyrithione, bacteria