An Analytical Survey of Trace Heavy Elements in Insecticides

There are many types of insecticides traded in the local and international markets, which vary depending on the type of target insect (e.g., whether crawling or flying). This paper aimed to assess the concentration of trace elements present in the various pesticide formulations (solid, liquid, and gaseous). This study was conducted in two groups: the first group was comprised of zinc, copper, iron, chromium, phosphorus, selenium, and cobalt; the second group included four heavy toxic elements (arsenic, thallium, lead, and mercury). These elements were analyzed by inductively coupled plasma/optical emission spectrometry (ICP-OES).


Introduction
With the growth of the world population, food production will need to increase by more than 60%, assisted by the safe and effective use of pesticides. Pesticides have an important role in helping to eliminate insects that destroy crops or cause epidemics diseases [1][2][3][4][5].
The increase in the use of pesticides often results in many adverse impacts, especially on the agricultural environment [6,7]. For this reason, various analytical techniques are used to test pesticides, including chromatographic methods [8,9]. Pesticides are widely used [10] in agriculture, medicine, and industry and have the potential to change the ecosystem [11]. Pesticides contain active ingredients and are used to ensure that high agricultural yield and quality can be achieved, but can cause environmental pollution if used incorrectly [12]. Organophosphorus pesticides (e.g., tebufenozide, chromafenozide, methoxyfenozide, and acetonitrile) [13] target those pests affecting fruit and vegetable crops, such as apples, grapes, cucumbers, cabbage, tomatoes, and spinach [14].
Some pesticides have large effects on mental and reproductive health and the developmental neural degenerative diseases among pregnant women and children [1,4,9]. If the percentage of pesticide toxicity dose increases, it leads to asthma and anaphylaxis in the human nervous system [9,15].
Pesticide alternatives often reduces the need for pesticides, including systemic insecticides, which are highly effective in the elimination of crop pests, using biological soil, pest-resistant tools, and fatty acid salts (potassium salts) [16]. Pyrethroids are used as an alternative to highly toxic pesticides and are inexpensive [17,18]. Neonicotinoids, alternatives to pesticides, are widely used in agriculture and are highly water-soluble [19]. Many pesticides and heavy metals are durable and nonbiodegradable and can accumulate along biological chains (soil, plants, food, and seawater) [20]. Therefore, the presence of large amounts of pesticides and heavy metals in the environment represents a risk to human health and the environment. For this reason, accurate monitoring of these concentrations plays an important role [21]. The literature cites many methods for heavy metal determination in soils, phosphorus rocks, seawater, plants, biologic materials, steel, and cast iron, including inductive coupled plasma-mass spectrometry [22], inductive coupled plasma atomic emission spectrometry [23], atomic absorption spectrometry with flame or electrothermal atomization [24], electrochemically with ultramicroelectrodes [25], and anodic stripping voltammetry [26].

Preparation of Samples.
In the case of solid samples, 1.0 g was dissolved in 10 mL distilled water and filtered. For the liquid samples, 1.0 g of each sample was mixed with distilled water to a final volume of 10 mL. For the gaseous samples, the aerosols were collected from the packets by spraying in the separation funnel, and equal amounts of distilled water were added. The mixtures were shaken well and allowed to separate overnight. The aqueous layer was then isolated from the funnel and filtered.

Precautions.
No heating or acid digestion was performed due to the volatility of the samples. To accurately determine the dissolved elements, the samples were filtered using a 0.45-m membrane.

Data Analysis and Calculations.
The measurement units for the assessed samples (solid, liquid, and aerosol) are microgram per liter (ug/L) or Parts Per Billion (ppb). For trace elements with zero ppb, these were considered as "nondetectable", meaning that the analyte concentration/intensity was negative or that the analyte concentration is below the method's detection limit.

Results and Discussion
Some of the trace (zinc, copper, iron, chromium, phosphorus, selenium, and cobalt) and heavy (arsenic, thallium, lead, and mercury) elements in solid, liquid, and gaseous pesticides species were determined by spectrometry. This study focused on the three insecticide categories consisting of six liquid, six solid, and four gaseous samples. Among the liquid insecticides samples, selenium, arsenic, and mercury were not detected (Table 1 and Figure 1). The concentrations of the other elements (Zn, Cu, Fe, Cr, P, Co, Tl, and Pb) varied. Among the solid pesticide samples, zinc, phosphorus, selenium, arsenic, thallium, and mercury were absent (Table 2 and Figure 2). On the other hand, it was found that most of the samples of gaseous pesticides are free of all studied elements,     (Table 3 and Figure 3). The zinc, copper, iron, chromium, phosphorus, cobalt, thallium, and lead elements were detected in all liquid insecticide samples (Table 1). Among the liquid insecticides, the zinc concentration was highest in CyperCel (2389 ppb) and Clash (1078ppb) and lowest in Brodor (10ppb). Zinc, copper, iron, chromium, cobalt, and lead elements were detected in all of the solid insecticide samples (Table 2). Among the solid insecticide samples, the lowest detectable concentration of zinc was found in Madar (10 ppb (Table 3). Zinc element was found only in one insecticide sample (Paygon for creeping insects, green, 52 ppb). The iron content was highest in the Raid insecticide (150 ppb) and lowest in Paygon for creeping insects (green). Both chromium and phosphorus were detected only in the Raid insecticide (33 and 20 ppb, respectively). Thallium was detected in two samples [Pif Paf (19 ppb) and Paygon for flying insects (blue)]. The lead concentration was highest in the case of Raid (62 ppb), but was not detected for Paygon for flying insects (blue).
The impacts of the active substance in different insecticides and in different kinds of insecticide (liquid-solid, solidgas, solid-liquid) are listed in Table 4.
(i) Active Substances in the Similar Insecticide Types. Among the liquid insecticide samples, the zinc concentration was highest in CyperCel (2389 ppb) and Cyper Safe (968 ppb), lowest in Paygon for creeping insects (green) (52 ppb), and absent from the solid insecticides. The percentages of copper element are 464 ppb and 669 ppb in case of the two liquid pesticide samples Cyper Safe and CyperCel, respectively. The concentration of copper became lower in case of the solid samples Acefed (19 ppb) and Lanid (128 ppb), respectively, but the copper ratio is nil for the gaseous samples. The concentration of iron element is increased in both liquid and solid insecticide samples, while it has a nil or 10 ppb concentration in the Pif Paf and Paygon gaseous pesticide samples, respectively. The percentage of chromium element is detected in case of the liquid and solid pesticide samples with different ratios, but it has a nil ratio in gaseous samples. The concentration of phosphorus ratio is nil in case of solid and gaseous pesticide samples, while it was presented in one of the liquid insecticide samples, CyperCel (377 ppb). Selenium and mercury elements were detected in none of the three pesticide types (liquid, solid, and gas). Cobalt was present in the three samples at 1-18 ppb. Thallium was detected in one of the gaseous samples (Pif Paf, 19 ppb). Lead was present in the three cases of pesticide samples with different ratios. It has a higher concentration in case of the liquid samples than in solid insecticide samples, while it was present in gaseous samples with lower ratio.
(ii) Active Substances in the Different Insecticide Types. The highest percentage of zinc element is presented in case of Clash (1078 ppb) liquid insecticide in comparison with Pif Paf solid insecticide sample. The highest ratio of copper element is present in case of Probalt (179 ppb) solid insecticide sample in comparison with a liquid sample (Brodor, nil percentage). The iron ratio was higher in the solid sample (3655 ppb, Probalt) than in the liquid sample (664 ppb, Brodor) and, paradoxically, the ratio of iron in liquid Clash was higher than in Pif Paf solid (3676 ppb vs. 102 ppb). The chromium ratio has a 85 ppb in case of Probalt solid insecticide sample. This ratio is higher than liquid Brodor insecticide sample (16 ppb). Paradoxically, it was found that the ratio of chromium in case of liquid Clash sample (73 ppb) is higher than solid Pif Paf sample (nil). The phosphorus element ratio is only present in case of Brodor and Clash liquid insecticide samples as 80 ppb and 842 ppb, respectively. The cobalt element is present in case of the Clash liquid sample (39 ppb) with moderate ratio but it has a lower ratio in case of the solid and gaseous samples. The percentages of selenium, arsenic, and mercury elements are nil in case of the three (liquid-solid, solid-gas,  International Journal of Analytical Chemistry solid-liquid) samples. The thallium ratio is only found in one liquid sample (Brodor, moderate ratio, 92 ppb). Lead element was present in the three cases with different ratios. It has a higher concentration in case of the Clash liquid sample (1316 ppb) rather than the solid and gaseous insecticide samples. The studied insecticides were divided into three groups: insect insecticides, insecticides, and insecticides for all types of insects. For the tested creeping insect insecticides, Sniper had the highest concentration of elements (Table 5). For flying insect insecticides, the liquid Brodor insecticide contained a higher concentration of elements than the biodegradable insecticide. Also, we found that the liquid insecticides contained higher concentrations of elements than the solid and gaseous pesticides. When comparing insecticides from the same case and product, it can be concluded that the Paygon for insects is more likely to occur in the appearance and concentration of elements. When comparing the different physical formulations, the Pif Paf solid concentrates contained copper and iron elements rather than the Pif Paf gas vaporizer samples. We tested the effect of the odor ratio on pesticides using two types of liquid and cruciferous insecticides (of the same composition and active substance). Compared to CyperCel odor, the element concentrations were lower in the Cybersif syrup insecticide.

Data Availability
The data used to support the findings of this study are available from the author upon request.

Conflicts of Interest
The author declares no conflicts of interest.