**1. Introduction**

Fenthion (*O,O*-dimethyl *O*-(4-(methylthio)-*m*-tolyl) phosphorothioate) is a contact and stomach systemic organophosphorus pesticide, used as a wide-spectrum insecticide for numerous crops against many suckings and biting pests. It was developed in 1960 and first commercialized by Bayer Agriculture in the USA as an insecticide/acaricide for mosquito and insect control that is commercially available worldwide in several formulations [1].

Microalgae are important inhabitants of aquatic ecosystems, where they fulfill critical roles in primary productivity, nutrient cycling, and decomposition. Detrimental effects of pesticides on algae may have subsequent impacts on higher trophic levels [8]. It has been well established that changes in the macromolecular composition of phytoplankton species or shifts in community composition can affect the growth rate of zooplankton grazers [9]. Unquestionably, aquatic environments receive direct and indirect pesticide inputs, inevitably exposing microorganisms to pesticides. Millions of pounds of active pesticide ingredients are applied in coastal watersheds each year, and in addition, pesticides may affect marine inhabit-

Toxic Effects of the Organophosphorus Insecticide Fenthion on Growth and Chlorophyll…

http://dx.doi.org/10.5772/intechopen.72321

119

Toxicity data involving ecotoxicology of fenthion toward nontarget microorganisms are limited. Most studies have focused on microbial degradation and biotransformation of fenthion rather than impacts on natural microbial populations and communities. Furthermore, studies of fenthion effects on soil microbes are far more common than studies of toxicology assessments in aquatic environments. Published data regarding marine or estuarine microorganisms are

The aims of the present survey were (i) to assess the acute toxicity of the organophosphorus insecticide fenthion toward nontarget aquatic microorganisms, such as marine algae, (ii) to investigate the possibility of using the parameter of chlorophyll pigments as biomarkers of exposure to fenthion, (iii) to compare the observed and predicted endpoint toxicity data and evaluate the predictive capability of two QSARs based on physicochemical properties of target organic toxicant (n-octanol/water partition coefficient and water solubility), and (iv) to predict the toxicity of 13 principal metabolites and degradation products of fenthion toward

*Tetraselmis* is a genus of a marine, motile, green phytoplankton (Prasinophyceae) that has very high lipid levels and also contains natural amino acids that stimulate feeding by other marine animals [12]. For this reason, it is used as a food source for feeding marine crustaceans, especially shrimp and mollusks. *Tetraselmis suecica* (Kylin) Butcher [12] (formerly known as *Platymonas suecica*, by Kylin, [13]) is a free-living, flagellate species that was initially isolated from seawater of the English and Swedish coasts, but later research has suggested that it is probably cosmopolitan [14]. The unicellular marine microalga *T. suecica* that is used in the bioassays of the present study is a strain of phytoplankton that is commonly cultivated in shellfish husbandries [15] and has been routinely cultivated by our laboratory [16]. This species was chosen because it is easy to be cultivated [15], and its response in toxicity tests is

Unialgal cultures of the species were maintained in liquid *f/*2 growth medium as recommended by Provasoli-Guillard National Center for Culture of Marine Phytoplankton (CCMP) [17]. More specifically, the selected strain of microalga was cultured in natural seawater, which had been

ants via spills, runoff, and drift [10].

the selected marine microalgae.

**2. Materials and methods**

highly reproducible [16].

**2.1. Organism and culture conditions**

even scarcer [11].

In Greece, only one formulation of fenthion was registered by Bayer CropScience Hellas, with the trade name LEBAYCID 50% EC (containing 50% w/v fenthion as the active ingredient), which is classified as dangerous for humans, but is not classified for aquatic organisms [2]. This insecticide is extremely effective in controlling the major insects infecting olives, such as the olive fruit fly *Bactrocera oleae (Dacus)*, the olive kernel borer or olive moth *Prays oleae*, the black scale *Saissetia oleae (Olivier)*, and *Margaronia* sp. and other masticatory insects. Although *B. oleae* is considered the most serious insect, all aforementioned insects are widely distributed in the Mediterranean region and occur on olives at population densities causing important economic losses. Therefore, fenthion was for many years one of the most commonly used pesticides in Greek territory and in the Mediterranean area generally [2].

The available information on the production and use of pesticides in general and hence of organophosphates as well is limited, fragmentary and in some cases unreliable [3]. On the basis of the limited information received from the Mediterranean countries, fenthion was one of the important compounds used during the 1980s and 1990s among other organophosphorus pesticides [3]. According to data provided by the Greek Ministry of Rural Development and Food, it appears that the quantities of fenthion that were used for agricultural purposes during the years 1983, 1984, 1985, 1986, 1987, 1988, and 1989 in Greece were 216,892; 409,139; 24,359; 197,843; 87,787; 160,433; and 213,514 tons of active ingredient, respectively [3].

Since June 2007, fenthion is no longer approved by the Greek Ministry of Rural Development and Food because of an excess number of poisoning-related events and ecotoxicology effects on nontarget organisms (Greek Ministry Decision, Register Number 122914–27/4/2005, 2005), apart from its 120 days of exceptional authorization (from May 1, 2009 to August 31, 2009) in accordance with Art. 8(4) of Directive 91/414/EEC for the treatment of olive trees against *Dacus oleae* (Greek Ministry Decision, Register Number 128569–11/5/2009c IN, 2009).

Although fenthion was developed as a safe pesticide because it is not easily converted to the possibly highly toxic oxon derivative (fenthion oxon) in mammalian species, however according to relative literature, many of its metabolites were detected in various plants, animals, and environmental matrices [4–7]. Kitamura et al. demonstrated that the in vivo metabolism of fenthion in fish leads to the formation of two metabolites, fenthion sulfoxide and fenthion oxon [4], while other studies proved that fenthion and its oxidation products were accumulated in fish [5]. Oxidation products of fenthion, including fenthion oxon, were also detected in house mosquitoes exposed to fenthion [6]. It has also been reported that fenthion was converted to fenthion oxon in the aqueous environmental bodies [7]. On the contrary, the toxicity and the metabolism of this organophosphorus insecticide have not been extensively studied in aquatic microspecies, such as microalgae.

Microalgae are important inhabitants of aquatic ecosystems, where they fulfill critical roles in primary productivity, nutrient cycling, and decomposition. Detrimental effects of pesticides on algae may have subsequent impacts on higher trophic levels [8]. It has been well established that changes in the macromolecular composition of phytoplankton species or shifts in community composition can affect the growth rate of zooplankton grazers [9]. Unquestionably, aquatic environments receive direct and indirect pesticide inputs, inevitably exposing microorganisms to pesticides. Millions of pounds of active pesticide ingredients are applied in coastal watersheds each year, and in addition, pesticides may affect marine inhabitants via spills, runoff, and drift [10].

Toxicity data involving ecotoxicology of fenthion toward nontarget microorganisms are limited. Most studies have focused on microbial degradation and biotransformation of fenthion rather than impacts on natural microbial populations and communities. Furthermore, studies of fenthion effects on soil microbes are far more common than studies of toxicology assessments in aquatic environments. Published data regarding marine or estuarine microorganisms are even scarcer [11].

The aims of the present survey were (i) to assess the acute toxicity of the organophosphorus insecticide fenthion toward nontarget aquatic microorganisms, such as marine algae, (ii) to investigate the possibility of using the parameter of chlorophyll pigments as biomarkers of exposure to fenthion, (iii) to compare the observed and predicted endpoint toxicity data and evaluate the predictive capability of two QSARs based on physicochemical properties of target organic toxicant (n-octanol/water partition coefficient and water solubility), and (iv) to predict the toxicity of 13 principal metabolites and degradation products of fenthion toward the selected marine microalgae.
