Key word5 parathion. toxaphcne, 2,J-D, pesticidal mixtures. general toxicity, cholinesteraw. SGPT, pentobarbit,llinduced sleep, pentobarbitdl tissue level5
The toxicity of the mixtures of parathion (PA), toxaphene (TOX) andlor 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in ICR male mice (21-24 g) by oral intubation, in corn oil, daily for up to 14 days. On Day 15, the exposure was discontinued, and animals were monitored for an additional period of 7 days for the possible reversibility of the toxicity. The body weight gain decreased with the mixtures, as well as with the individual agricultural chemicals (ACs), during the 14-day period. The cholinesterase (ChE) activity in the serum and brain was inhibited in the animals of the groups of PA (1-10 mg kg-') and PA (5 mg kg-')containing mixtures. TOX (50-200 mg kg-') caused initial inhibitory effects of 2045% on the serum ChE (Day 1) beforte producing increases of 5344% in the enzyme activity by Day 15, with little effects on the brain ChE levels. 2,4-D (50-200 mg kg-l) resulted in significantly elevated levels of the serum ChE, with substantial decreases in the brain ChE activity. The serum glutamic pyruvic transaminase level was up (38430%) in TOX (50 mg kg-'), 2,4-D (50 mg kg-') or their mixture group. No pathological changes at the light microscopic level in the brain and liver were noticed. TOX and TOX-containing mixtures significantly increased the livedbody weight ratio and decreased the pentobarbital (60 mg kg-', i.p., in saline)-induced sleep. When TOX (50 mg kg-') and PA (5 mg kg-') + TOX (50 mg kg-') groups were examined, the dilatation of the hepatic endoplasmic reticulum was distinguished and the decrease in the level of pentobarbital in the serum, brain, liver and kidneys was noted. The effects produced by these chemicals singly, as well as by their mixtures, appeared to be reversible in nature. The toxic effects exhibited by the mixtures of PA (5 mg kg-I), TOX (50 mg kg-') and/or 2,4-D (50 mg kg-') were found to be the resultant of the effects showed by their components individually.
JNTKODUCTION
Pesticides are used i n huge amounts throughout the world. They are generally toxic to many non-target species and have the potential to become part of the environment to pose a health risk. The magnitude of the risk associated with the mixtures of these agricultural chemicals (ACs) is not well known. Therefore, more information is needed about the toxicity of the chemical mixtures.
Although several acute toxicity studies on the mixtures of ACs selected from the same group, i.e. organochlorine compounds (OCs) or organophosphorus compounds (OPs), have been conducted,'*' relatively few studies have been done on the mixtures of pesticides of different categories and/or chemical classes.7 The effects of pretreatments of animals with