1954 Environmental Toxicology and Chemistry, Vol. 16, No. 9, pp. 1954–1961, 1997  1997 SETAC Printed in the USA 0730-7268/97 $6.00 + .00 SERUM B ESTERASES AS A NONDESTRUCTIVE BIOMARKER IN THE LIZARD GALLOTIA GALLOTI EXPERIMENTALLY TREATED WITH PARATHION JUAN CARLOS SANCHEZ,MARIA CRISTINA FOSSI and SILVANO FOCARDI* Department of Environmental Biology, University of Siena, 53100 Siena, Italy (Received 30 September 1996; Accepted 19 February 1997) Abstract—Lizards (Gallotia galloti) were given either single or consecutive acute oral treatments of the organophosphorus (OP) insecticide parathion in two different experiments. Brain, serum, and liver microsomal esterase activities and liver microsomal monooxygenase activities were measured 6 and 24 h after the single acute treatment at each of four different doses (Experiment 1) or periodically up to 72 d after a number of consecutive acute treatments at two different doses (Experiment 2). Inhibition of serum butyrylcholinesterase (BChE) and carboxylesterase activities was observed in all treatment groups after 24 h and in the groups treated with 2.5, 5, and 7.5 mg/kg of parathion 6 h after treatment. Brain acetylcholinesterase (AChE) was inhibited at all doses after 6 h but only at the highest dose after 24 h. Highly significant nonlinear correlations, based on a piecewise linear regression model, were obtained between brain AChE activity and serum esterase activities at two sampling times after the single acute treatment. Liver microsomal carboxylesterase was found to be induced at the lower doses 6 and 24 h after treatment. Liver microsomal monooxygenase activity was higher 6 h after treatment than at 24 h, but the difference was not statistically significant. In Experiment 2, serum esterase activities recovered exponentially over a period of weeks. An increase in the recovery time to normal esterase activity was observed after each consecutive acute treatment. Brain AChE activity was inhibited at the end of consecutive administrations of parathion at the higher dose, and liver microsomal monooxygenase activity was inhibited at both doses. Symptoms of poisoning were observed in lizards treated with the higher dose of parathion, but no mortality was recorded. Two main conclusions can be drawn: (1) serum esterase activities recovered extremely slowly after acute treatment with parathion and even more slowly after consecutive acute treatments, and (2) there was a nonlinear correlation between the nondestructive biomarkers, serum ‘‘B’’ esterases, and the destructive biomarker, brain AChE, 6 and 24 h after exposure. These results suggest that G. galloti should be an ideal bioindicator organism to assess OP exposure in the Canary Islands instead of the birds commonly used for this purpose. Keywords—Lizard Parathion B esterases Recovery Nondestructive biomakers INTRODUCTION Since the introduction of the first commercial product in the 1940s, organophosphorus (OP) compounds have become the most widely used class of insecticides in the world. One of the reasons for their popularity as insecticides is the fact that unlike the organochlorine insecticides which preceded them, they are usually nonpersistent in the environment and generally do not bioaccumulate [1] but are often acutely toxic. The relatively short time of persistence of OP insecticides in the environment, acute exposure, and the variety of detoxifi- cation pathways in organisms [2] mean that detection by chem- ical analysis in nontarget organisms is not a simple task. The biomarker approach is particularly suitable for evaluating the exposure to or effects of this class of compounds [3,4]. Parathion (O,O-diethyl O-[4-nitrophenyl] phosphorothio- ate) is an OP insecticide used extensively in the Canary Islands (Spain) to control a variety of agricultural pests. The Canary Islands have a total surface of 7,500 km 2 , of which 190,000 hectares (ha) are farmed [5]. After tourism, agriculture is the largest economic sector of the Canary Islands. It is estimated that in the four islands that make up the province of Santa Cruz de Tenerife alone, 249.6 tons of insecticides are used every year. Parathion accounts for about 3.95 tons/year (School of Agricultural Engineering, Tenerife, Spain, unpublished data). It is applied as a spray to the leaves of various fruit and field crops, principally grapes, at an application rate of 0.3 to 0.6 kg of active ingredient/ha. * To whom correspondence may be addressed. Like all OP insecticides of the phosphorothionates type, para- thion is activated to paraoxon by the cytochrome P450-dependent monooxygenases in the organism [6]. The toxic effect of paraoxon is to inhibit the enzyme acetylcholinesterase (AChE, EC 3.1.1.7), a critical enzyme in cholinergic synapses and neuromuscular junc- tions leading to hyperactivity of the cholinergic pathways [7]. Acetylcholinesterase belongs to the group of hydrolase enzymes classified by Aldridge [8] as type ‘‘B’’ esterases, which are in- hibited by OP compounds. Determination of brain AChE activity and other types of B esterase activity is a widely accepted method of assessing exposure to OP insecticides and/or their effects on nontarget organisms [9–13]. There has been a recent increase in the number of ecotox- icological studies based on nondestructive biomarkers (NDBs), particularly serum B esterases [4,14–17]. Avian serum butyr- ylcholinesterase (BChE, EC 3.1.1.8) has been proposed as a NDB because of its elevated sensitivity to inhibition by OP insecticides and because it can be measured easily by non- destructive methods. The limitations of BChE include its rapid recovery rate [12,14,15,18,19] and its wide variation between individuals [3,12,16, 18,19]. Attempts have been made to solve these problems. Fairbrother et al. [17] demonstrated that vari- ation in the plasma cholinesterase (ChE) levels in a given individual are much less than the variation between individuals and that statistical tests, such as covariate analysis, can be used as an appropriate method to analyze data. Sequential sampling of plasma ChE in the same organism is therefore a convenient method of investigating the percentage of inhibition resulting from exposure to OPs. A new approach based on immuno-