Fugacity Based EQC Level II Method: Prediction of Environmental Partitioning of a Fungicide Fluopyram

A fungicide Fluopyram has been subjected to an EQC Level 2 calculation using a fugacity-based environment model. According to the model, Fluopyram tends to build up in similar amounts in both soil and water. Sediment, soil, water, and air are predicted to contain the high concentration of the chemical. Fluopyram will be lost primarily by reaction (55.9%) and advection from water (39.7%). An overall residence time of 845 hours (35.3 days) is predicted by the model, as well as reaction and advection residence times of 1403 hours (58.5 days) and 2122 hours (88.4 days), respectively. Fluopyram is therefore not expected to be environmentally persistent, and reaction is predicted to be the key factor in the overall persistence. Fluopyram has a very low potential for atmospheric transport as only a very small portion of the chemical (2.42 x 10−03%) is predicted to leave the model environment in the advecting air


Introduction
Pesticides are widely acknowledged to play an important role through agricultural production due to their ability to reduce agricultural product losses while also improving overall yield as well as food quality [1].In the last ten years, at least 105 pesticides have been introduced or are in development: twenty one herbicides, one safener herbicide, thirty four insecticides/acaricides, six nematicides, forty three fungicides, and more [2].Numerous diseases are caused by pesticides [3].
Pesticides degrade as well as dissipate in farms after they are used, polluting ground water, air, soil, and rivers.Environmental fate models aid in estimating concentrations of pollutants in various environmental compartments [4].
Fluopyram, figure 1 is a Succinate Dehydrogenase Inhibitor (SDHI) fungicide that is used to control a variety of fungal infections and nematodes in plants [5,6].It is applied by spraying on foliage or soaking the soil.Its IUPAC name is N-(2-[3-chloro-5-(trifuoromethyl)-2-pyridinyl] ethyl)-2-(trifuoromethyl) benzamide originally developed by Bayer AG, Germany [7].It is primarily used to control grey mould as well as powdery mildew in grapes, but it is also used against fungi to regulate fungal infections in a variety of crops [8].It is somewhat soluble in water and has a low volatility.Fluopyram has poor acute toxicity to birds and mammals, but it is highly toxic to fish [9].

Figure 1. Fluopyram Structure
Given the significance of the Fluopyram in agriculture and in the absence of extensive experimental data on Fluopyram, this study aims to understand how physical-chemical properties of Fluopyram, control environmental fate parameters such as partitioning, transformation, and persistence using a "fugacity-based Equilibrium Criterion" Model (EQC Model) Level II [10].

Methodology
A Level II model explains a dynamic environment with chemical inflows and outflows through the compartment such that the different phases are all in equilibrium with one another at any given time.The total chemical within the environmental region of interest may vary over time due to two general processes: a) Advection; a chemical is transmitted into or out of the area of interest by the flow of a supporting medium; b) Degradation and chemical reactions; which result in a change in the overall chemical properties.There is no need to describe which compartment the chemical is introduced into, under this assumption [11].
Table 1 and table 2 show the important properties that influence Fluopyram fate and are referred to as model inputs [9,12,13].
For a multicomponent system the common fugacity, f is defined as the  = / (1) where, I = Total input rate = Direct Emission Rate + Advective Inflow Rate (2) Di is the overall D value for removing from a specific compartment by advection and chemical change.
The equilibrium assumption lets us determine a single fugacity that's constant throughout all compartments for such system. = /( + ) (3) where zi is fugacity capacity of particular phase for chemical.All simulations assumed a 1000 kg.h -1 emission rate to the model system with zero advection inflow concentrations through both water and air compartments.

Results and Discussion
Chemicals like Fluopyram which are of Type 1 with measurable vapour pressures, aqueous solubilities, and octanol-water partition coefficients, are expected from partition to some extent to available environmental compartments.Fluopyram's low vapour pressure results in a small percentage partitioning to air compartment (3.29 x 10 -3 %).Fluopyram is a moderately hydrophobic compound with a Kow value of 3.30.It will disperse into organic phases like soils and sediments.
Table 1 shows that Fluopyram is a moderately hydrophobic compound (Kow= 3.3) with a low water solubility (16.0 g.m -3 ).It is anticipated that it will partition to phases which contain organic matter such as soils and sediments as well as inorganic phases such as water.It is important to note that air-water partition coefficient is low (1.22 x 10 -08 ), and that the Henry's Law constant, which indicates a chemical's potential to volatilize from water into the atmosphere, is also very low.As a result, Fluopyram is unlikely to evaporate from water.
Figure 2 depicts the model output for Fluopyram emitted to air, water, and soil.Approximately 52% (4.39 x 10 5 kg) and 47% (3.98x 10 5 kg) are found in soil and water, respectively and 1% (8316 kg) in sediment as shown in figure 2 and figure 3.In comparison, Level I calculations had shown 63%, 36% and approximately 1% Fluopyram distributions in soil, water and sediment compartments respectively [14].Simulations were also carried out with 100 ng.m -3 Fluopyram in air together with 0 ng.L -1 Fluopyram water; also with 0 ng.m -3 of the chemical in air together with 100 ng.L -1 of the chemical in water.Whether the chemical (Fluopyram) enters the system through advection via water or air, the model predicts the same percentage distribution and various loss processes of the chemical.
The Fluopyram was predicted to have an overall chemical residence (τo) of approximately 35.2 days, figure 2. The reaction residence times (TR) were predicted to be approximately 58.45 days and the advection residence times (TA) were predicted to be approximately 88.41 days.
The product of the volume (V, m 3 ) and the fugacity capacity of the compartment determines the capacity of a given compartment to accumulate the chemical (Z).As shown in table 3, the VZ (water) is 6.72 x 10 15 and the VZ soil is 7.42 x 10 15 indicating that soil has approximately 1.10 times the capacity of water to accommodate Fluopyram.The different advective as well as reactive losses from various environmental compartments are depicted in detail in figure 2. The most common loss mechanism in the air compartment is reaction is 8.00 x 10 -3 %; reaction is the most common loss mechanism in the water compartment that is 55.9%; reaction is the most common loss mechanism in the sediment compartment that is 0.0223%.The only loss mechanism from the soil compartment is reaction (4.10%), because there is no advection in this compartment.Overall, reaction loses 60.2% of the chemical while advection loses only 39.8%.

Conclusion
The EQC Level II model, fugacity-based environmental model was applied for Fluopyram.Fluopyram is predicted to accumulate in soil and water to similar quantities, according to the model.The chemical is expected to be present in high concentrations in water, sediment, soil, and air.It is lost primarily through reaction and advection from water.Fluopyram is not expected to persist in the environment.Only a trace of the chemical is expected to escape from the model environment in the advecting air.

Figure 2 .
Figure 2. Results of the EQC Level-II simulation represented diagrammatically.

Figure 3 .
Figure 3. Fluopyram's relative distribution among the four environmental media

Table 1 .
Physico-Chemical values used as Input for Fluopyram

Table 2 .
Half-life parameters for Fluopyram used as Level II Input

Table 3 .
Fugacity capacity, amount and concentration of Fluopyram in different environmental phases.