Inhalation toxicity studies of Thimet (Phorate) in the male swiss albino mouse, Mus musculus: II. Lung histopathology, pseudocholinesterase level and haematological studies M. Morowati* Cell research centre, 19, Joag path, Pune-4110019 India Received 12 January 1998; accepted 9 May 1998 Abstract Sub-chronic exposure of the male swiss albino mouse, Mus musculus to the recommended ®eld dose of Thimet (Phorate; 6728.5 mg m 3 ) in a whole-body inhalation chamber was studied on the 2nd, 4th, 6th, 8th, 10th and 12th week of exposure. A signi®cant depression of pseudocholinesterase (Che) level was observed throughout the experimental period. A signi®cant decrease in hae- moglobin concentration (Hb conc.), red blood corpuscle count (RBC) count and packed cell volume percent (PCV%) was observed from the 6th week of exposure until the end of the experiment. Total leucocyte count (WBC count) showed a signi®cant rise in the 2nd week of exposure (this rise was due to the rise in the monocyte and neutrophil counts), and later from the 6th week onwards showed a signi®cant decrease until the end of the experiment (the decrease was mainly due to the fall in the lymphocyte count). The lung in the exposed animals showed various degrees of bronchopneumonia, emphysema and collapse throughout the experiment. After a 30 day recovery period almost all the blood parameters were back to the normal levels, except the total leucocyte count which showed a higher level than the normal count. However, the lung in the recovered animals showed emphysematous changes but no bronchopneumonia and in¯ammation. The results suggest that inhalation of the pesticide, Thimet could cause damages to Mus musculus, it also suggest that the improper handling and usage of this pesticide by human beings could aect their well being and eciency at work. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Organophosphates; Inhalation toxicity; Lung histopathology; Pseudocholinesterase level; Haematology 1. Introduction In developing countries labour is cheaply available, and they are exploited for the application of pesticides without any protective measures (mask, gloves, etc.). This way they may be exposed to a large amount of pesticides which they imbibe by various routes. Thimet (O,O-diethyl-S-(ethylthiomethyl)phosphoro- dithioate), is one such organophosphorus insecticide (OP) which is being used for the control of a large number of agricultural pests. It emits a strong mercap- tan odour and has a signi®cant volatisation ability (Jury et al., 1984). Hence the workers are subjected to inha- lation of Thimet vapours, and dermal contact, and oral intake is possible, should their contaminated hands come in contact with their mouth. A review of the literature reveals many studies on the eects of OP insecticides on human beings as well as animals (Kennedy et al., 1970; Wicker et al., 1979; Coye et al., 1987; Hassan et al., 1991; Dutta et al., 1993; Yeary et al., 1993). However, in almost none of these investigations, the inhalation route of exposure is con- sidered. In the present work animals were exposed to Thimet in a whole body inhalation chamber which according to Gage (1970) and Ecobichon (1992) may actually constitute a mixture of inhalation (maximum amount), dermal contact and oral intake (to a lesser extent). This way a human exposure situation is almost mimicked. 2. Materials and methods Seventy-two, 5-week-old male swiss albino mice, Mus musculus were purchase from the National Institute of Virology (NIV), Pune, India. They were randomly 0269-7491/98/$Ðsee front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(98)00111-0 ENVIRONMENTAL POLLUTION Environmental Pollution 103 (1998) 309±315 * Corresponding author. 29 Syrus Lane, Shademan Street, Shariaty Avenue, Tehran 15647, Iran. Fax: +98-21-7528641.