Toxic effects of acephate on Paramecium caudatum with special emphasis on morphology, behaviour, and generation time J. Venkateswara Rao * , K. Srikanth, S.K. Arepalli, V.G. Gunda Toxicology Unit, Biology Division, Indian Institute of Chemical Technology, Hyderabad 500 007, India Received 4 January 2006; accepted 9 February 2006 Available online 23 March 2006 Abstract The continuous increase in the number of new chemicals as well as the discharges of solid and liquid wastes triggered the need for simple and inexpensive bioassays for routine testing. In recent years, there has been increasing development of methods (particularly rapid tests) for testing environmental samples. This paper describes the quick toxic evaluation of an organophosphorus insecticide, ace- phate (O,S-dimethyl acetylphosphoramidothioate) on Paramecium caudatum for acute and sub-acute toxicity studies with reference to morphology, behaviour, and its generation time. The lethal concentrations for 10 min and 2 h were determined by probit method, as 500 mg L 1 and 300 mg L 1 , respectively. Higher concentrations of 10 min exposure caused cell lysis with disintegration of cell mem- brane and precipitation of protoplasm. Combination of conventional light microscopy and computerized video tracking systems were used to study the locomotor behaviour of paramecia. The test organism was under stress and exhibited an initial increase and subsequent decrease in the swimming speed when exposed to 1/4, 1/2, 3/4, and LC 50 concentrations for 10 min (125, 250, 375, and 500 mg L 1 , respectively). Similar changes were also noticed when paramecia were exposed to LC 50 for 2 h. In a separate set of experiments, the num- ber of generations and generation time in 24 h was evaluated with respect to the different sub-lethal concentrations (30, 60, 120, and 240 mg L 1 ). The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic poten- tial of insecticides. The major advantages associated with these tests are: they are inexpensive, simple, user-friendly, space saving, and seem to be attractive alternatives to conventional bioassays. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Paramecium caudatum; Acephate; Cell lysis; Cytotoxic; Morphology; Behaviour; Generation number and time 1. Introduction The extensive use of organophosphorus insecticides, dur- ing the past decades has led to a number of negative effects on terrestrial and aquatic organisms. Insecticides are being used in agriculture and they are found to be more hazardous than herbicides and fungicides. Acephate (O,S-dimethyl acety- lphosphoramidothioate) a water soluble organophosphorus insecticide registered to control certain insect pests on a variety of field, fruit, and vegetable crops, in food handling establishments, on ornamental plants both in greenhouses and outdoors with residual systemic activity. Acephate and its primary metabolite, methamidophos, are toxic to various species. A number of studies were conducted on the toxicity of acephate on different organisms and indicated as a potent neurotoxicant [1]. It is also found to be mutagenic [2], carcin- ogenic [3], and cytotoxic [4]. Monitoring of aquatic ecosys- tem pollution represents one of the major activities involved in measures aimed at environmental protection. Usage of non-targeted organisms in environmental tox- icology is needed to understand the wide range of toxic effects caused by the pesticides on different organisms [5]. Fish and other aquatic biota that were commonly used as bioindicators of persistent organic pollutants [6] have been 0048-3575/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.pestbp.2006.02.005 * Corresponding author. Fax: +91 40 2719 3191/2717 3757. E-mail addresses: jv@iict.res.in, jv@india.com (J. Venkateswara Rao). www.elsevier.com/locate/ypest Pesticide Biochemistry and Physiology 86 (2006) 131–137 PESTICIDE Biochemistry & Physiology