A comparative photodegradation studies of methyl parathion by using Lumistox test and conductometric biosensor technique Sergei V. Dzyadevych a,b , Jean-Marc Chovelon a, * a Laboratoire d’Application de la Chimie a ` l’Environnement, UMR 5634, CNRS-Universite ´ Claude Bernard Lyon 1, 43, boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France b Laboratory of Biomolecular Electronics, Institute of Molecular Biology and Genetics, National Academy of Sciences of Ukraine, 150 Zabolotnogo Street, Kiev 03143, Ukraine Abstract The photodegradation of methyl parathion, and the toxicity assessment of the resulting mixtures including the main degradation photoproducts (methyl paraoxon and 4-nitrophenol) have been investigated. The degradation was studied by monitoring the change in compounds concentration as a function of irradiation time by employing HPLC analysis. Toxicity tests were performed by using a conductometric biosensor based on cholinesterases and a bioassay based on a luminescent bacteria Vibrio fischeri (Lumistox). It has been found in the case of biosensors that the strongest inhibitor of immobilised cholinesterases was the methyl paraoxon and a strong synergistic effect of methyl parathion and methyl paraoxon occurred. Other results were obtained using Lumistox test, since in this case methyl parathion is the most toxic compound for V. fischeri, and similar toxicity were obtained for both 4-nitrophenol and methyl parathion. These results indicate that effect of toxic compounds on the luminescent bacteria is not related to cholinesterase activity. Both tests could be very useful to control an organophosphorous pesticides degradation process. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Conductometric biosensor; Bioassay; Photodegradation; Methyl parathion; Methyl paraoxon 1. Introduction Many tones of pesticides are annually used in agriculture and horticulture which can be naturally degraded by differ- ent pathways such as microbial degradation, chemical hydrolysis and photodegradation. During these transforma- tion processes, intermediate products, which can be more toxic than the initial products, are generated. On the other hand, purification of waters polluted by these compounds can be attained by different treatments including, for example, Advanced Oxidation Processes (AOP). These treatments are theoretically capable of con- verting pesticides into ‘‘environmentally’’ harmless deriva- tive products but sometimes, here also, these products are more toxic than parent ones. In both cases, degradation products are generated and the lack of data concerning their toxicity becomes worrisome. Under these conditions, the number of pollutants can be very important and conven- tional analytical systems are no longer able to identify all of them. As a result, rapid and reliable analytical strategies are required to study and identify a wide variety of compounds. Consequently, it is necessary to develop toxicity tests that can give a much more selective information about the toxicity impact of water sample. This paper reports the photodegradation of methyl para- thion, and the toxicity assessment of the resulting mixtures using two toxicity tests: a conductometric biosensor techni- que and a bioassay test (Lumistox). The toxicity assessment of organophosphorous com- pound using conductometric biosensor is associated with their ability to inhibit enzymes such as the acetyl- or butyrylcholinesterase (AcChE or BuChE). Normally, AcChE and BuChE hydrolyze corresponding substrates, while acid and choline species are formed (cf. the reactions). Products of these reactions can be detected with ampero- metric [1,2], potentiometric [3,4], and conductometric [5] electrodes. In the presence of pollutants, an inhibition of enzymes occurs and decreased amount of products originat- ing from the enzymatic reaction is formed. The responses of the cholinesterase biosensors are thus compared with and without pollutants. 0928-4931/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0928-4931(02)00058-9 * Corresponding author. Tel.: +33-4-7243-2638; fax: +33-4-7244-8114. E-mail address: Chovelon@univ-lyon1.fr (J.-M. Chovelon). www.elsevier.com/locate/msec Materials Science and Engineering C 21 (2002) 55 – 60