State Enterprise “Scientific Center for Preventive Toxicology, Food and Chemical Safety named after Academician L. I. Medved of the Ministry of Health of Ukraine”, Kyiv, Ukraine
ABSTRACT. Objective. Analyse and summarize modern data on the degree of hazard of chlorpyrifos when used in accordance with the intended purpose, substantiate the expediency of limiting the scope and extent of use of insecticide in the human living environment.
Materials and methods. Analytical review of scientific publications has been performed using the abstract database of libraries and the text database of medical and biological publications PubMed.
Results. Based on the conducted analytical review of scientific publications, data on the degree of hazard of chlorpyrifos have been summarized, the requirements regarding the expediency of the prohibition of the use of chlorpyrifos and chlorpyrifos-based preparations as insecticidal agents in the human living environment, first of all, in everyday life, in maternity departments, in medical institutions, in child day care centres and educational institutions have been substantiated.
Keywords: chlorpyrifos, toxicological properties, human health, environment, nervous system, children, prenatal and postnatal development.
Relevance. The analysis of the list of insecticidal preparations and disinfectants based on them, which are allowed for use in Ukraine, intended to neutralize synanthropic insects in the human living conditions and in the living environment, has shown the presence of a significant number of preparations, the active ingredient of which is the organophosphorus compound, chlorpyrifos.
Chlorpyrifos was registered by Dow Chemical Company in 1965 as an insecticidal preparation and has since been widely used to destroy pests in agriculture and synanthropic insects in living conditions.
Currently, 248 insecticides were included in the List of pesticides and agrochemicals authorised for use in Ukraine — 37 chlorpyrifos-based preparations, including 11 preparative forms manufactured in Ukraine (Fig. 1) [1].
Preparative form: dursban, fosban, pirinex, sairen, derosgan, nurel-D, cipiplus, etc.
Fig. 1. Number of chlorpyrifos-based insecticides, included in the List of pesticides and agrochemicals authorized for use in Ukraine (2018)
The list of disinfection agents registered in Ukraine for the destruction of synanthropic insects in the living conditions (2011–2016) included 269 insecticides of various chemical groups, of which 10 were chlorpyrifos-based (Fig. 2) [2].
Fig. 2 Number of chlorpyrifos-based disinfection insecticide registered in Ukraine (2011–2016)
Chlorpyrifos exhibits high cost-effectiveness, while at the same time it poses a significant hazard to human health and environment. Its effect on the body, as with the majority of organophosphates, is associated with respiratory, endocrine, immune, nervous, and carcinogenic or mutagenic effects. Long-term experience with preparation accumulated numerous epidemiological data on the harmful effects of chlorpyrifos on the autoimmune processes of the body, as well as on the prenatal and postnatal development of the foetus/newborn/child.
Objective. Analyse and summarize modern data on the degree of hazard of chlorpyrifos when used in accordance with the intended purpose, substantiate the expediency of limiting the scope and extent of use of insecticide in the human living environment.
Materials and methods. Analytical review of scientific publications has been performed using the abstract database of scientific libraries and the text database of medical and biological publications PubMed.
Results. The conducted literature analysis has shown that chlorpyrifos [0,0-diethyl-O- (3,5,6-trichloro-pyridyl-2) -thiophosphate] as an active ingredient of organophosphorus insecticides is widely used in agriculture, in the practice of medical, sanitary and household disinfection to combat harmful synanthropic insects. For example, American farmers use about 2,270–2,720 tonnes of chlorpyrifos per year on dozens of crops, including almonds, apples, citrus, corn, and strawberries [3]. In Ukraine, 487 tonnes of chlorpyrifos-based insecticidal preparations based were just imported in December 2012 (for a total amount of USD 3,125 thousand) [4]. And this does not include domestic production.
In its appearance, chlorpyrifos is a white crystalline substance with a specific odour, stable in neutral and acidic media, is relatively quickly neutralized in alkaline medium. In comparison with other organophosphorus compounds, chlorpyrifos — the most stable in the environment, is adsorbed by an organic matter of the soil and maintains stability for 140–360 days [5-9].
When chlorpyrifos penetrates the insect body through the respiratory tract, stomach or external surfaces, it affects the activity of acetylcholinesterase, simulating acetylcholine, and block its action for a long time. Duration of insecticidal action of chlorpyrifos is 40–70 days [9]. According to another literary source, the protective effect against insects is reported within 2–3 weeks [10].
In humans and animals, chlorpyrifos, as a result of desulphurisation involving cytochrome P-450 of the liver (CYP2B6), is bioactivated on two main biologically active metabolites — chlorpyrifos oxone and 3,5,6-trichloro-2-pyridyl phosphate [11-15]. Chlorpyrifos oxone can bind to acetylcholinesterase and decrease its activity, causing cholinergic hyperstimulation of the nervous and muscular systems [11, 16-18]. By its effect on the nervous system, chlorpyrifos oxone is 3,000 times more active than chlorpyrifos [19].
The study of the toxicokinetics of chlorpyrifos in rats has shown that the preparation is excreted from the body of animals renally (from 86 to 93 %) and with faeces (from 6 to 11 %) [20]. The following metabolites are identified in urine: glucuronide — 3,5,6-trichloro-2-pyridinyl (80 %), 3,5,6, trichloro-2-pyridinyl (12 %) and 3,5,6-trichloro-2-pyridinyl glucoside (4 %). The tissues have traces of chlorpyrifos, as well as its metabolites: 3,5,6-trichloro-2-pyridyl phosphate (75–80 %), 3,5,6-trichloro-2-pyridinyl (15–20 %) [17,19,21,22].
Study of the distribution of chlorpyrifos in the rat body showed that the highest amount of the preparation was found in the adipose tissue, the elimination half-life of which is 62 hours, kidneys — 12 hours, skeletal muscles — 16 hours, liver — 10 hours. It is reasonably to note that the metabolites of chlorpyrifos in the body of other animals may differ from those found in rats. For example, the main metabolites of chlorpyrifos in the urine of cows are diethyl thiophosphate (35.9 % of the administered dose) and diethyl methyl phosphate (26.8 %); in faeces — 1.7 % of the unchanged form of the preparation [23].
Chlorpyrifos is excreted in milk of cows when it penetrates the body with feed in the amounts over 5.0 mg/kg. A three-fold treatment of cows with 0.15 % emulsion of the preparation was accompanied by its excretion in milk for 4 days or more (from 0.34 to 0.024 mg/kg). The final excretion of the preparation from the body lasts for 30 days [17, 19, 24].
Thus, the given data testify to the possibility of a potential hazard to humans when using products that are contaminated with chlorpyrifos.
Despite certain advances in the study of the peculiarities of body exposure to chlorpyrifos, the main mechanisms of its action on the human body have not been clarified. Analysis of current literature data suggests that the mechanism of the toxic action of chlorpyrifos is not limited to the anticholinesterase activity inherent in organophosphorus compounds. The pathogenesis of poisoning is combined with other biochemical processes in the body, which indicates the multi-vector nature of the mechanism of action [25-31]. Additionally to cholinesterase enzymes, other numerous potential molecular targets were discovered under exposure to chlorpyrifos. In particular, in vitro studies have shown the cytotoxicity of this compound, its effect on the synthesis of macromolecules (DNA, RNA, proteins), possible interaction with different enzymes [30, 32].
In case of poisoning with chlorpyrifos, it became clear that it could affect other neurotransmitters and enzymes at doses below those that substantially inhibit the activity of acetylcholinesterase [33-35]. Thus, in experiments on rats and cell cultures, it has been shown that chlorpyrifos can affect the level of serotonin, the activity of the serum protease enzymes [34-36]. Numerous studies suggest that chlorpyrifos can also lead to the formation of oxidative stress due to the metabolite of chlorpyrifos oxone. And oxidative stress itself is a significant toxicity factor [11, 15, 18, 37]. In this case, excessive formation of reactive oxygen species occur in the body, which leads to the development of lipid peroxidation syndrome and includes the following pathological components: damage to membrane lipids, impaired processes of cell division and phagocytosis, and changes in the structural and functional organization of membranes. It is also known that poisoning of the body with chlorpyrifos, especially in acute forms, can cause the occurrence of hypoxic states [34, 39-41].
Symptoms of poisoning when chlorpyrifos penetrates the human body through the respiratory organs are usually accompanied by bloody nasal secretions, runny nose, cough, chest discomfort, and difficulty in breathing. And when it penetrates human body through the skin, localized sweating and involuntary muscle contraction were reported. Contact of the preparation with mucous membranes of the eye can cause pain, bleeding, lacrimation, blurred vision [17, 34, 42-44].
The effect of chlorpyrifos on human health depends on the amount of substance, multiplicity and duration of action [20, 44-47]. Studies in volunteer found that 24 hours after inhalation exposure of chlorpyrifos to the body at a concentration of 80.4 mg/m3 for 4 minutes, decreased activity of acetylcholinesterase in blood plasma by 84–85 % was reported, while the activity of the enzyme in red blood cells was not changed. Recovery of the specified values occurred within 96 hours.
For all other routes of exposure to the human body, other systemic toxic effects may develop within 12 hours and manifest as pale skin, sweating, nausea, vomiting, diarrhoea, abdominal cramps, headache, dizziness, eye pain, lacrimation, salivation, etc. At the same time, the effect on the central nervous system is manifested by incoherence, abnormalities of speech and reflexes, weakness, fatigue, muscle contraction, tremor, and ultimately paralysis of the limbs and respiratory muscles. In severe cases, involuntary defecation or urination, mental disorders, arrhythmias, loss of consciousness, convulsions and coma may also occur. Out of the 439 cases of chlorpyrifos poisoning, there were 35 deaths among people (8 %). Death came within five days of exposure to the preparation (in 42 % due to respiratory failure or cardiac arrest) [42-45].
In experimental conditions on animals, the toxic properties of chlorpyrifos were studied in different ways of substance administration.
Species-specific sensitivity of animals to the toxic effect of the preparation has been determined: LD50 for rats was determined at the level from 82 to 270 mg/kg, mice — 60–152 mg/kg, guinea pigs — 500 mg/kg, rabbits — 1,000 mg/kg, and sheep — 800 mg/kg. Mice were the most sensitive to the action of the preparation. Specie-specific sensitivity factor is 15.6 [7-9, 16, 17, 48, 49].
In addition, there is dependence not only on the species of animals but also on their genotype. Upon application of chlorpyrifos on the skin of animals, LD50 for Sprague Dawley rats was determined at 1,000 mg/kg; for Hemalay rabbits — 1,233 mg/kg, for New Zealand rabbits — 5,000 mg/kg [7-9].
It was established that contact of chlorpyrifos with gastrointestinal tract of rats is manifested by respiratory distress, decreased motor activity, ataxia, sanious secretion from eyes and nose, exophthalm, tremor of muscles, paresis of hind limbs, frequent urination, diarrhoea.
Inhalation exposure of insecticide to the body of rats or rabbits (exposure of 4 hours) is manifested by ataxia, humped body position, respiratory distress, exophthalm, salivation, tremor, seizures, paresis of hind limbs. LC50 of chlorpyrifos for female rats has been established at the level from 2.01 to 4.16 mg/L, for male rats — 4.07 mg/L, for rabbits — more than 0.2 mg/L [16,17].
In case of contact with skin and mucous membranes of the eyes of New Zealand rabbits, chlorpyrifos causes poorly expressed irritation of the skin and moderately pronounced irritation of mucous membranes of the eyes [7, 8, 48].
In experiments on guinea pigs, no sensitizing properties were detected. Cumulative properties of chlorpyrifos are moderately expressed [5].
Thus, according to DSanPiN (State sanitary Standards and Rules) 8.8.1.002-98, toxicity parameters of chlorpyrifos, depending on the routes of contact with the body, belongs to the following classes of danger: for inhalation exposure — 2nd, for oral — 3rd, for dermal — 4th; for irritating action on the skin — 3rd, for mucous membranes of the eye — 2nd, for cumulative properties — 3rd, for sensitizing properties — 4th.
During a study on 3 species of animals: rats, mice and dogs — the values of LOEL and NOEL of chlorpyrifos were determined under conditions of subacute, subchronic and chronic experiment [7-9, 16, 48, 50-53].
NOEL for Wistar rats at inhalation exposure (2 weeks, 6 hours a day, 5 days a week) has been established at 10 mg/m3 (with a decrease in the activity of acetylcholinesterase in the rat brain by 50 %).
NOEL for Fisher rats, when applied on the skin (21 days, 6 hours a day, 5 days a week), has been established at 5.0 mg/kg (maximum of the studied doses).
For CD-I mice, which received chlorpyrifos with feed for 28 days, LOEL has been established at 15 ppm (2.7 and 3.4 mg/kg for females and males, respectively) by a decrease of acetylcholinesterase activity in plasma (by 75–90 %) and in red blood cells (40–50 %). Body weight loss has been also reported in males.
In the Fisher rats, which received preparation with feed in the following doses: 0.1, 1.0, 5.0 and 15.0 mg/kg for 13 weeks, doses of 5.0 and 15.0 mg/kg showed decreased acetylcholinesterase activity in the brain and red blood cells, as well as pathohistological changes in the adrenal glands. NOEL – 0.1 mg/kg. In another experiment on Charles River rats (receiving chlorpyrifos with feed for 13 weeks), NOEL was established at 0.03 mg/kg (by a decrease in acetylcholinesterase activity in red blood cells and plasma).
For CD-I mice that received the preparation with feed in a subchronic experiment (13 weeks), the NOEL was established at 0.7 mg/kg (inhibition of acetylcholinesterase in red blood cells and biosubstrates).
In a chronic experiment for CD-I mice, which received the preparation for 18 months, NOEL has been established at 0.7 mg/kg by the inhibition of brain acetylcholinesterase activity.
In Fisher 344 rats, which received chlorpyrifos with feed (0.05, 0.1, 1.0 and 10.0 mg/kg) for 2 years, reduced body weight gain, inhibition of acetylcholinesterase activity in plasma, red blood cells and brain were reported for the concentration of 10 mg/kg. In males, the changes were more pronounced than in females. NOEL — 0.1 mg/kg [26].
In a 2-year experiment in Beagle dogs, NOEL was established at 0.01 mg/kg (by anticholinesterase effect).
In the literature, summarized results on the carcinogenic activity of the preparation [50, 53, 54] are presented in two types of laboratory animals, rats and mice. Oncogenicity was not reported in any of the studies conducted:
- in an experiment in rats, which received chlorpyrifos with feed for 104 weeks at the doses of 0, 0.01, 0.03, 0.1, 1.0 and 3.0 mg/kg body weight, NOEL was established at 0.1 mg/kg body weight (by the criterion “reduction of acetylcholinesterase activity in plasma, red blood cells and brain”);
- in an experiment in Fisher rats, which received chlorpyrifos with feed for 104 weeks at the doses of 0, 0.05, 0.1, 1.0 and 10.0 mg/kg body weight, NOEL was established at 0.1 mg/kg body weight (by the criterion “reduction of acetylcholinesterase activity in plasma, red blood cells and brain”);
- in experiments in CD-I mice, which received chlorpyrifos with feed for 104 weeks at concentrations equivalent to 0, 0.5, 5.0, 15.0 mg/kg body weight. Oncogenicity of chlorpyrifos has not been established [55, 56].
Genotoxicity of chlorpyrifos in mutagenicity tests, namely: in the Ames test, a recombinant test on yeast, point-mutation induction tests in the culture of Chinese hamster ovary cells CHO/HGPRT, chromosomal aberrations, and sister chromatid exchanges with and without metabolic activation have not been reported. Also, genotoxicity in the micronucleus test in mice is not determined [56].
At the same time, independent studies have found that chlorpyrifos exhibits mutagenicity on Drosophila cells, leads to an increase in the number of cells with structural disorders in chromosomes [57, 58], increase in chromosomal aberrations and sister chromatid exchanges in bone marrow cells of mice and lymphocytes in vitro [59 - 61], hypomethylation, and DNA structure violations [62]. In addition, many studies indicate genotoxicity of chlorpyrifos in plants, fish, and mushrooms. However, US EPA experts do not take this data into consideration, although their Californian colleagues have come to the conclusion on possible genotoxicity of chlorpyrifos [56, 63]. In our opinion, under certain conditions, chlorpyrifos may exhibit genotoxicity.
The EPA, EC and WHO experts classified chlorpyrifos as a substance for which the absence of carcinogenicity in humans was proved (Group E), taking into account the results of carcinogenicity tests in chronic animal experiments (rats and mice) and the results of genotoxicity tests [64].
However, epidemiological studies have established a correlation between the incidence of lung and rectum cancer and exposure to chlorpyrifos [65, 66]. There was also insignificant increase in the risk of developing glioma [67], breast cancer [68], prostatic cancer[69] and non-Hodgkin’s lymphomas [70] in farmers who used chlorpyrifos-based preparations. These works caused a lively discussion in the literature [71]. A weak power of the used statistical methods, as well as the lack of assumptions about the mechanisms of development of these tumours, did not allow the use of epidemiological data as unconditional evidence of chlorpyrifos carcinogenicity for humans.
EPA experts have suggested that the oncogenicity mentioned may not be related to the chlorpyrifos themselves but to the components of the preparative form. In this regard, it is planned to continue the study of the carcinogenic properties of chlorpyrifos.
The teratogenic activity of chlorpyrifos was studied on 3 types of laboratory animals: mice, rats, and rabbits [72-78].
In the experiment in female Wistar rats, which received chlorpyrifos intragastrically from 6 to 15 days of gestation at doses of 0, 0.3, 3.0 and 6.0 mg/kg body weight, it was found that chlorpyrifos at a dose of 6 mg/kg exhibited toxicity in pregnant females (reduction of activity of acetylcholinesterase in serum) and foetotoxicity (decrease in average weight and body length of foetuses, increase in the number of foetuses with delayed ossification of the skeleton, decrease in the parameters of behavioural reactions in young rat); t a dose of 3.0 mg/kg, chlorpyrifos does not have a toxic effect on the body of pregnant females, but causes an embryotoxic effect (increase in the number of post-implantation losses) and a foetotoxicity (increase in the number of foetuses with a shortening of 13th pair of ribs, with a rudimentary 14th pair of ribs, wavy ribs, with delayed ossification of the skeleton). Chlorpyrifos at a dose of 0.3 mg/kg does not show toxic effects on the body of pregnant females, does not cause embryotoxicity and foetotoxicity. The teratogenic effect of chlorpyrifos was not detected in any of the doses studied [73, 74].
When the chlorpyrifos was administered to the body of pregnant female rats from 6 to 15 days of gestation at the doses of 0, 0.1, 3.0 and 15.0 mg/kg, the females showed a decrease in feed consumption, a decrease in body weight gain, a decrease in the activity of acetylcholinesterase in red blood cells in the medium and higher doses. NOEL for females is 0.1 mg/kg (by inhibition of red blood cells acetylcholinesterase), NOEL for foetal development — 15.0 mg/kg [75].
In another experiment in CD rats, chlorpyrifos (purity of the preparation was 96.1 %) at the doses of 0, 0.5, 2.5 and 15.0 mg/kg was studied in the period from 6 to 15 days of gestation. The action of the preparation in a dose of 15.0 mg/kg manifested as toxic effect in females and increase in post-implantation mortality of embryos. NOEL for females and foetal development is 2.5 mg/kg.
Study of the toxicokinetics of chlorpyrifos (97 %) in foetuses of rats, which received the substance throughout the entire perinatal development showed that the level of chlorpyrifos in the organs was (ng/g tissue) the following: in the liver — 0.0531, in the brain — 0.364 [76]. It was found that in the placenta chlorpyrifos was determined at the level of 0.040 ng/g tissue, in amniotic fluid — 0.0010 ng/mL (Fig. 3). These data, as well as data from other researchers, indicate the ability of chlorpyrifos to penetrate blood-brain barrier [77].
Fig. 3. Toxicokinetics of chlorpyrifos in foetuses of rats, which received chlorpyrifos from 0 to 20 days of gestation
In the experiment in NZW rabbits, chlorpyrifos was studied (purity of the preparation was 96.1 %) at the doses of 0, 1.0, 9.0, 81.0 or 140.0 mg/kg in the period from 7 to 19 days of gestation. There was a toxic effect in pregnant females (decrease in body weight gain), foetotoxicity (decrease in the length and weight of the foetus, abnormalities of ribs, scoliosis) at the doses of 81.0 and 140.0 mg/kg. NOEL for pregnant females and foetal development is 9.0 mg/kg [75].
In the experiment in CF-1 mice, which received chlorpyrifos at the doses of 0.1, 1.0, 10.0 and 25.0 mg/kg for 10 days, NOEL for foetal development was established at 10.0 mg/kg (decrease in body size at a dose of 25.0 mg/kg), NOEL for pregnant females — 0.1 mg/kg (decreased activity of acetylcholinesterase in plasma and red blood cells in the range of doses of 1-25 mg/kg) [75].
It is important to note that not only chlorpyrifos but also its main metabolite — 3,5,6-trichloro-2-pyridinyl (TCP) was studied on two types of laboratory animals. In the study of the effect of TCP (99.7 % purity) on embryogenesis of rats at the doses of 50, 100 and 150 mg/kg from 6 to 15 days of gestation, New Zealand rabbits, which received a substance from 7 to 19 days of gestation at the doses of 0, 25, 100 or 250 mg/kg, NOEL was established for pregnant female rats and foetal development at 100 mg/kg; NOEL for pregnant female rabbits at 100 mg/kg (body weight loss for pregnant females at a dose of 250 mg/kg), NOEL for foetal development - 25 mg/kg [78].
Neurotoxicity of chlorpyrifos was investigated in experiments in rats, chickens and mice [74, 79-89].
When the chlorpyrifos penetrated the body of adult rats at the doses of 10.0, 50.0 and 100.0 mg/kg, the symptoms of neurotoxic activity in the medium and higher doses were reported. It was manifested by myasthenia, decrease in motor activity, and abasia. These symptoms were more pronounced in female rats. In this case, histological tests did not found damage to the structure of the nervous tissue. NOEL for rats is 10.0 mg/kg.
Intermittent effect in the experiment (30 days of administration, then a 2-weeks pause) with oral chlorpyrifos effect at the dose of 2.5 mg/kg on the body of the rats manifests by the effect on neurotrophin receptors and cholinergic proteins. Such neurochemical changes may lead to impairment of functioning of the nervous system [83].
In the experiments in Leghorn chickens under conditions of acute and subchronic experiment (13 weeks, doses of 1.0 5.0 and 10.0 mg/kg), no manifestations of remote neurotoxicity was reported [87, 88].
The analysis of literature data also showed that a considerable number of studies have been carried out to determine the prenatal effects of chlorpyrifos on the state of the nervous system in the postnatal period. Data obtained in recent years, suggesting that the oxone metabolite affects the neuronal cytoskeleton, destroying all three cytoskeleton paths. These violations occur at the level of expression of cytoskeleton proteins, intracellular distribution, post-translational modification, dynamics and function of cytoskeleton, which in turn can affect both neuronal and glial cells [79]. At the same time, it was observed that the influence on the behaviour of animals does not depend on the way insecticide penetrates the body.
As a result of the studies of behavioural responses in female Wistar rats, which received intraperitoneal chlorpyrifos from 6 to 15 days of gestation at the doses of 0, 0.3, 3.0 and 6.0 mg/kg body weight, disorders of higher nervous activity of young rats, which were born from females on the dose of 6.0 mg/kg were detected. For example, in a 3-week male young rats of this group, there was a decrease in motor activity (the number of crossed squares is less by 52.5 %, vertical stacks — by 48.7 %, halt observations — by 47.3 % compared to the control group, p < 0.05). Changes in behavioural reactions were less pronounced in females than in males. In the study of a 2-month male young rates born from females receiving chlorpyrifos at the dose of 6.0 mg/kg, the decrease in motor activity remained at the same level as in a 3-week young rats (the number of crossed squares is lower by 55.1 %, vertical stacks - by 51.2 %; halt observations — by 49.5 % compared with the control group, p < 0.05). The revealed changes in the young rat show evidence of the development of inhibitory processes in the central nervous system, which in the prenatal period were subjected to chlorpyrifos at the dose of 6.0 mg/kg. It should also be noted that for this group of animals there is a clear relationship between the decrease in the activity of serum acetylcholinesterase in pregnant females, body weight and length of the foetuses with manifestation of a violation of behavioural reactions in the young rats, in which inhibitory processes were observed in the central nervous system [74].
In another experiment, the increased motor activity of mice from female CD-1 mice at day 17 after birth was observed following oral administration of chlorpyrifos to pregnant females at the doses of 3.0 or 6.0 mg/kg. Depressive responses to sensory stimuli were detected only at day 27 after birth. The decrease in the activity of acetylcholinesterase in the blood and brain was statistically dependent on the preparation dose. The majority of effects were observed in mice (males and females) at the dose of 6.0 mg/kg, and the dose of 3.0 mg/kg induced behavioural changes only in females [80].
Following subcutaneous administration of the preparation at a dose of 0.2 mg/kg in rats, functional changes of the central nervous system manifested by violation of spatial orientation were observed [80, 83].
Studies by T. L. Lassiter in vitro showed that neonatal tissue acetylcholinesterase was more sensitive to chlorpyrifos than enzyme/tissue of adults [84].
Animal experiment also showed that the prenatal effects of chlorpyrifos are manifested by deviation in the development of the brain, as well as a number of behavioural disorders in the postnatal period and even in adulthood [82]. In animals there were changes in the level of anxiety, motor activity, decrease in sexual differences in behaviour [75, 80]. Due to the detection of sexual differences in behaviour, some researchers consider chlorpyrifos as a substance that can cause neuroendocrine disorder [85]. Moreover, individual studies have shown that chronic poisoning with low doses of chlorpyrifos in female rats, even a few months before pregnancy, was manifested by the symptoms of hyperactivity in the offspring [83, 86].
The neurotoxic activity of chlorpyrifos was also investigated in an experiment in CD-I mice, which received oral chlorpyrifos both at prenatal (from 15 to 18 days of gestation at the doses of 0, 3.0 or 6.0 mg/kg) and postnatal periods (postnatal days 11 to 14, doses of 0, 1.0 and 3.0 mg/kg). Four months later, increase in the incidence of cardiovascular diseases in females, which received a prenatal dose of 6.0 mg/kg, and changes in the social behaviour of animals was observed [89].
Data from epidemiological studies on the adverse effects of chlorpyrifos on prenatal and postnatal foetal/newborn/child development were of particular concern. Foetal maldevelopment associated with the effect of chlorpyrifos on the body during pregnancy include: reduction of body weight at birth and decrease in growth rates, reduction of head size, impaired behavioural reactions in the neonatal period [90 - 93].
For 10 years in three groups of cohort studies of pregnant females and their children, the relationship between levels of chlorpyrifos or its metabolites in maternal urine or in the umbilical cord blood and the results of the development of nervous behaviour were studied [90, 91]. The results of epidemiological studies conducted at the Center for the Environment and Children’s Health (Columbia, USA) indicate that in 18.3 % of umbilical cord blood samples, chlorpyrifos content exceeded 6.17 pg/g of plasma [94].
Newborns born from females with detected levels of chlorpyrifos in the blood had a developmental disorders - reduced body weight at birth by 67.3 g and body length by 0.43 cm [92]. During epidemiological study at another Center for the Environment and Children’s Health (New York), 404 pregnant females who had contact with chlorpyrifos during pregnancy showed such parameters as presence of metabolite-3,5,6-trichloro-2-pyridinyl (TCPD), the activity of the hydrolytic enzyme paraoxonase PON1; in newborns — body weight and body length, head size, gestational age [93]. It was found that the average values of TCPD in the maternal urine were 7.6 μg/L (fluctuations of the parameter from 1.6 to 32.5 μg/L). The activity of paraoxonase in the urine of pregnant females has been reduced, and this parameter had a correlation with body weight loss and reduction of the length of the body and with a decrease in the size of the head of the newborns [95].
Data on the effect of chlorpyrifos on behavioural responses in children born from mothers in whom the preparation or its metabolites were detected in different biological samples have been also analysed. Follow-up of the children was conducted for 12, 24 and 36 months, and “Mental and psychomotor development index of children” were determined. For example, delay of mental development of children increases with age, at the same time, the state of motor activity recovers. The use of software applications in the studies has shown that increase in chlorpyrifos metabolites in the prenatal period predicts an increase in the probability of clinical manifestation of the syndrome of reduction of memory and motor activity at the age of five. Such children had a delayed reaction, it was more difficult for them to perform tasks related to short-term memory, they showed the development of mental diseases or delayed development. If the influence of chlorpyrifos on newborns manifests itself in the development of abnormal reflexes, then in adolescence it may cause the development of emotional and psychological problems [96, 97]. It should be noted that these effects are more pronounced in boys than in girls [98]. Similar study findings were obtained in Thailand [99].
In the US, chlorpyrifos has been restricted for use in domestic conditions since 2000, and in 2002 it was prohibited due to the suspicion of childhood leukemia, effects on reproductive and immune systems [100]. At the same time, the consequences of its use for children under the age of puberty continue to manifest over time [93].
Recent studies conducted using magnetic resonance imaging have shown changes in the brain of boys and girls exposed to chlorpyrifos during intrauterine development. They manifested as a disorder in the development of the brain, which areas are responsible for attention, decision-making, speech, self-control, and short-term memory [98, 101]. Recent studies by Silver MK have shown that the negative prenatal effects of chlorpyrifos may cause disruption of visual and auditory development in childhood. This, in turn, will negatively affect the cognitive development of the child [102].
Given the potential danger of chlorpyrifos for the body, its use in residential areas is unacceptable.
According to the literature, when conducting hygienic tests of the air of residential areas in a house in Western Australia, the average concentration of chlorpyrifos was 2 times higher than the established hygienic rate - 0.001 mg/m3 [103]. Also, chlorpyrifos was detected in 100 % of air samples from 12 houses located along the Arizona-Mexico border [104]. In the air of a room in Jacksonville (Florida, USA), different average amount of chlorpyrifos is determined depending on the season of the year: in summer — 366.6 ng/m3, in autumn — 205.4 ng/m3, in winter — 120.3 ng/m3 [104].
When conducting air tests of the rooms in New York, where pregnant African-American and Dominican females lived, the presence of chlorpyrifos was detected at the level of 99.7 % of 337 air samples at an average concentration of 3.0 ng/m3 [105].
It was also established that chlorpyrifos is an integral part of household dust at an average concentration of over 400 ng/m3 in buildings after treatment with preparations [106]. In 20 out of 26 samples of dust sampled in a farmer residential house in Oregon, chlorpyrifos was found at a concentration of 0.20 μg/m3. The examination of residential houses by the Department of Housing and Urban Development found that chlorpyrifos in the air was detected in 78 % of 479 samples at an average of 0.50 ng/m3 [107].
Taking into account the fact that after disinsection measures in the living conditions, people of different age categories and health (pregnant females, children, elderly people, suffering from bronchial asthma, allergies) can be exposed to the effects of the preparation. The literature provides a significant number of references to the impact of chlorpyrifos on the body of farm workers, as well as the population living near cultivated land, as well as people who consume products with residual amounts of chlorpyrifos. Such an effect may lead to a disturbance of the functioning of the nervous system, which manifests as a deterioration in the memory in adults.
The influence of chlorpyrifos on pregnant females may lead to the development of such dangerous diseases as autism, hyperactivity syndrome, attention deficit disorder in children, tremor, Parkinson and Alzheimer disease in adulthood [75, 94, 108-112]. Also, the effect of the microdoses of chlorpyrifos on the foetus in the mother's womb is also dangerous [113, 114].
Therefore, the considerable range, wide scope of the use of the preparation, which is characterized by environmental resistance, its ability to form highly toxic (biologically active) metabolites in the body in the process of biotransformation that have the properties to pass through blood-brain and placental barriers, showing multi-vector toxic effects on the body, especially harmful effect on prenatal and postnatal development of the foetus, manifested by a decrease in body weight at birth and decrease in growth rates, decrease in head size, impaired behavioural responses in the neonatal period are important criteria of danger of the insecticide. The presence of changes in the brain of children exposed to chlorpyrifos during intrauterine development were confirmed by the results of studies using magnetic resonance imaging. They manifested as a disorder in the development of the brain areas which are responsible for attention, decision-making, speech, self-control, and short-term memory. If the influence of chlorpyrifos on newborns manifests itself in the development of abnormal reflexes, then in adolescence it may cause the development of emotional and psychological problems.
According to EU Directive (76/464/EC), requirements of WHO, US EPA, DSanPiN 8.8.1.002-98 chlorpyrifos is classified as hazard class II. The European Commission labels chlorpyrifos with the following symbols: S ½, S 45, S 60, S 61, T: R 25, N:R 50, R 53.
Consequently, determination of the negative effect of chlorpyrifos as a result of the long-term use of its considerable amount in various spheres of agricultural production, as well as in everyday life, on the health of people of different age groups, especially females and children, raised the question of the feasibility of further use of this pollutant as the problem of state level. Reduction of the range and volume of insecticides on its basis, with the subsequent prohibition on the use of this preparation is an urgent need for time. In some countries of the world, laws have been adopted to restrict the use of chlorpyrifos, first of all, in everyday life.
Guided by the urgency of protecting children and farmers associated with the possibility of exposure to chlorpyrifos in the regions of residence with the use of insecticide, the Democrats of the US Senate proposed to adopt a draft law Protect Children, Farmers, and Farmworkers from Nerve Agent Pesticides Act , 2017, regarding the prohibition of use of chlorpyrifos [115].
Considering the above, the Governor of the Hawaiian Islands, David Ige, signed a new law on June 13, 2018, which gradually cancels the use of chlorpyrifos in the country, and also increases the regulation of other restricted pesticides [116]. Since the preparation is an integral part of household dust, which in these conditions becomes an additional factor of exposure to chlorpyrifos on the human body, it is inadmissible to use it in residential areas for the control over of synanthropic insects that have a sanitary-epidemiological significance.
The above is the reason for the necessity of prohibiting the use of chlorpyrifos and preparations based on it as insecticide means for the control over synanthropic insects in the field of human living environment, first of all, in everyday life, in maternity wards, in health care institutions, in day care centres, and in educational institutions of Ukraine.
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