Investigation of acute toxicity of (2,4-dichlorophenoxy)acetic acid (2,4-D) herbicide on crayfish (Astacus leptodactylus Esch. 1823)
Introduction
Among herbicides widely used, with potential toxicity against humans, are phenoxy compounds such as (2,4-dichlorophenoxy)acetic acid (2,4-D); (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T); (4-chloro-2-methylphenoxy)acetic acid (MCPA) and their respective esters. Among these 2,4-D is the most widely used herbicide in the world [1]. 2,4-D is a systemic herbicide and is used to control many types of broadleaf weeds. It is used in cultivated agriculture, in pasture and rangeland applications, forest management, home, garden, and to control aquatic vegetation. 2,4-D functions by maintaining high levels of the plant hormone auxin, resulting in overstimulation of plant growth and ultimately death. Historically, the product Agent Orange, used extensively throughout Vietnam, was about 50% 2,4-D [2].
Data on the aquatic toxicity of 2,4-D on non-target organisms is either incomplete or lacking. Although some formulations of 2,4-D were reported highly toxic to fish; others were less so. Limited work have been carried out on ecotoxicology concerning invertebrates of the ecosystem. There are studies in the literature concerning the accumulation of 2,4-D, its derivatives, and other agricultural chemicals in tissues [3]. Oruc and Uner [4] studied the combined effects of 2,4-D and azinphosmethyl on antioxidant enzymes for clarifying mode of action of these chemicals.
Farah et al. [5] studied acute (96 h) toxicity and stress behavior of 2,4-D on freshwater fish (Heteropneustes fossilis, Clarias batrachus, Channa punctatus) as LC50 values as 81, 122, 107 mg/L; while they calculated 48 h LC50 to mosquito larvae (Culex pipiens fatigans) 302 mg/L. Fish displayed behavioral changes such as restlessness, swimming at the surface or abnormal swimming behavior, vigorous jerks of body, loss of balance, myotonia and anorexia. Breathing difficulties and respiratory problems were also encountered both in fish and mosquito larvae. Papaefthimiou et al. [6] studied physiological mechanism of toxic action of 2,4-D in frog, honeybee and beetle heart and reported heart of frog and honeybee to be extremely sensitive.
Potential genotoxic effects have been reported by various workers: mice in vivo [7]; cultured mammalian cells [8]; freshwater fish C. punctatus with micronucleus test [9]; induction of micronuclei and erythrocyte alterations catfish, C. batrachus [10]; micronucleus test in human lymphocytes [11]; apoptic effects and DNA degradation in walking catfish, C. batrachus [12].
In addition to its mechanism of action on plant growth hormones, it is known that 2,4-D provokes changes in the animal nervous system based on complex formation with acetylcholine, and thus inhibition of acetylcholinesterase (AChE) activity and also increase of the level of another neurotransmitter serotonin. Decreased acetylcholinesterase activity of human erythrocytes (in vitro) due to indirect membrane modification and increased reactive oxygen species has been reported by Bukowska et al. [13].
This study was conducted to determine the acute toxicity of 2,4-D, most widely used herbicide in the world, on a widely distributed, important invertebrate in many aquatic systems: the narrow clawed crayfish (Astacus leptodactylus Esch. 1823) using the static test system.
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Materials and methods
Crayfish (A. leptodactylus Esch. 1823) were obtained from a local breeder. The test organisms (average weight 23.5 ± 1.49 g; average length 9.6 ± 0.21 cm) were transported to the laboratory in appropriately wetted plastic containers and immediately transferred to the test aquaria (n = 6) and allowed to acclimatize for 48 h. Twenty liter-capacity aquaria containing 10 L water were used as test chambers. At the time of dosing air was turned off; it was on at all times otherwise. Water temperature,
Results and discussion
The calculated 96 h acute LC50 value (95% confidence limits) of technical 2,4-D, using a static bioassay system to crayfish (Astacus leptodactylus) was 32.6 mg/L (95% confidence limits: 15.10–327.16). Control mortality was zero. The results show that 2,4-D is toxic to crayfish. Crayfish is a recommended test organism according to the reference/standard methods [14], [15] and the Turkish national regulation [16]. Results appear in Table 1 and Fig. 1.
Green and Abdelghani [18] investigated the
Acknowledgment
The authors thank the U.S. E.P.A. for making available the acute toxicity testing probit analysis computer program.
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