Organophosphate Esters (OPEs)

Posted: January 5th, 2023

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Organophosphate Esters (OPEs)

Background information

In the field of insecticide use and agriculture, organophosphates have been on the rise in the last fifteen years. This is due to the phasing out of the polybrominated diphenyl ethers (PBDEs) in 1978 because they increased milk production in lactating and pregnant mothers as well as disruption of the thyroid hormones among the expectant women and newborns (Wang et al., 215). Similar to the most functional groups, the organophosphates occur in various forms. For instance, they can occur in biomolecules such as DNA, RNA, with inclusion of insecticides and flame- retardants. The halogenated hydrocarbons are used as flame-retardants, while the non-halogenated are used as plasticizers and lubricants. The widespread use of the compounds as Flame-retardants results from the substitution of the highly regulated bromine compounds. The low cost of production associated with organophosphates and the compatibility nature of the combination drives the use of the compounds their benefits in furniture, textile electronics, and flame-retardants (Wang et al., 215). The physical addition of the organophosphates compounds in the various final products rather than chemical addition poses excellent environmental and health risks due to the leaking action to the environment through abrasion, volatilization, and leaching step. Whenever the organophosphates are used, and fire cases arise, the non-halogenated react forms a polymeric form of phosphoric acid, which shields the oxygen by forming a char layer. On the other hand, Halogenated compounds respond in the same manner, although the decomposition to radicals to lower the fire spreading poses a health risk (Wang et al., 215). Furthermore, organophosphate use is a matter of concern due to the high frequencies and concentration of the organophosphate concentration in air, dust, water, and biota samples.

Physical characteristics

The organophosphates exhibit a variety of physical characteristics. The odor of the organophosphates is described as a garlic or petroleum-like scent, making it possible to diagnose its effluent into the environment. (Nartop et al., 956) The organophosphates, as additives, diffuse at various rates in regards to vapor pressure and an ambient temperature of the surrounding air. The highly volatile organophosphates have been ruled to exist in the gaseous phase. The organophosphates containing a higher molecular mass live as suspended particular matter in the air and dust. The various organophosphate flame retardants exist at a concentration of less than ng m-3 to several ug m-3 (Nartop et al., 956). The organophosphates make up a specific composition of the gas in pubic and domestic buildings and the various diverse building materials and consumer products.

Chemical properties

The various chemical characteristics associated with the organophosphates are responsible for the different reactions of the organophosphate compounds. The organophosphate’s chemical structure comprises the phosphoryl group that consists of the terminal oxygen connected to the phosphorous through a double bond (Wang et al., 28). There are two lipophilic groups bonded to the phosphorous molecule within the structure, hence leaving a halide group connected to the phosphorous. The organophosphates chemically dissolve in water and are dispersed freely through dissolution, abrasion, and volatilization. The organophosphates’ chemical structure gives the polar characteristic to the organophosphate compounds (Blum et al., 640). The lipophilic and the hydrophobic types of organophosphates are the most widely used types. The effectiveness of organophosphates’ use is directly proportional to the increasing number of halogen atoms in a molecule. This indicates the molecules with a higher number of halogens to be highly effective, especially in the manufacture of the flame-retardant (Wang et al., 28). The gaseous and solid-phase organophosphate flame-retardants are highly effective in the prevention of the spread of fire. This is because the organophosphates in the solid phase form a char on the burning component. In contrast, in the gaseous phase, they react by removing the H+ as well as OH- radicals from the flammable gases through the reaction with the Br and Cl atoms hence lowering the rate of combustion.

Biological transport of contaminant

Various pesticides present various effects on human beings and animal health. This is owed to their capability of interaction between the pesticides and the endocrine system in both human and animal health (Sühring et al., 7410). It is evident in the insecticides’ ability to be transferred directly from nursing mothers to their children via breastfeeding. The early studies in the 1970s proved the organophosphates to be moderately toxic hence the declination of the tasks in the 1990s without much research on the increasing use of the organophosphates at various toxicity levels (Sühring et al., 7410). Carbamates present a correlation to the organophosphates in the mode of action. However, they have some disparities in the dosage required to project the minimum poisoning as well as translate to mortality where the dosage for the carbamate compounds is higher than the organophosphates in human beings.

Since the organophosphate chemicals are neurotoxic, their mode of action is based on inhibition of the acetylcholine esterase in both the central and peripheral nervous systems, resulting in choline and acetate formation. Therefore, this translates to the enhancement of the nerves and consequently their blocking. The suppression’s net result is the convulsion, paralysis, and death for both human beings and insects (Sühring et al., 7410). The organophosphate also presents higher chances of Genotoxicity as well as carcinogenic effects, which increase the various rates of cancer cases in modern society. Some of the cancer cases associated with organophosphates include lymphoma, leukemia, brain tumors, and lymphoma. Human beings get exposed to the organophosphates directly from the air or through the feed on contaminated foods. For instance, fish are affected by the organophosphates when they leak into the water system; hence the feeding of the fish in contaminated water bodies translates to adverse effects on human health (Sühring et al., 7410). This is because the organophosphates are not broken down in the fish. Human beings can also get exposed to organophosphates by feeding on improperly washed vegetables harvested before the chemicals are diffused out.

Bioaccumulation in biota

The increased leaching of the organophosphates into the water system and indoor and outdoor endanger human beings. For instance, the accumulation mechanisms of the organophosphates in fish are unknown. The bioaccumulation of the organophosphates varies with tissues with muscles containing the lowest organophosphate concentration while the liver has the highest concentrations, such as TPP and TCEP (Ding et al., 105919). The highest levels, as well as lowest levels, are, however, carried over generations. Organophosphate biotransformation is usually associated with polychlorinated alkyl moieties (TDCIPP) and arly moieties (TPHP and TCP) which lead to accumulation of organophosphate rather than those organophosphates linked with alkyl or short chain chlorinated moieties.

Organophosphates Arctic Samples

Similarities

Both Guo and Suhring, investigated the trends and the long-range transport potential of the Organophosphates. From both the study projects by Suhring and Guo, the findings showed that organophosphate esters transportation occurs on the surface water rather than the sediment.  The study finding at the various sampling sites illustrated that various agricultural activities, agricultural production, and waste effluents play a significant part in the transport of the organophosphates in a freshwater environment.

Differences

The Suhring et al. (7410) study is based on the yearly ship sampling, which was conducted in 2007-2017 and involved two-land stations in the Canadian Arctic. The project postulations are the result of the filter fraction of 117 air samples. In the study by Suhring, the chlorinated and alkyl Organophosphate flame retardants formed the principal compounds in sediment with tris(2- chloroisopropyl) phosphate with concentrations of 3.37-29.65 ng/g. the study also examined the relationship between the organophosphate flame retardants with total organic carbon contents in the sediments (Suhring et al. 7410). The whole organic carbon relationship with the organophosphate flame-retardants was read from the survey, with the results indicating a direct correlation.

The Guo et al. (9) postulates, on the other hand, are based on the organophosphate flame retardants detected in the surface water, suspended sediments as well as river sediments for a study conducted in Yangtze river in China. . According to Guo et al. (9) the concentrations of the Organophosphate flame-retardants from the six locations are estimated to range from 8.99 to 112.45ng/L. From the study, Guo et al., (9) argue that the organophosphate flame-retardants concentrations in suspended sediments are related to the sediment particle size distribution. From the study, Guo et al. (9) detected four organophosphate esters in the 97% samples, seven in 50% or fewer samples, while three were not detected. The findings from the study Guo indicate the media concentrations for the organophosphates esters for total summation as 237 ship and 50pg m-3 for land-based samples. The individual median concentrations for ethanol, 2-chloro-, phosphate was indicated from below detection to 119pg m-3. The study’s higher engagement projected to 2340pg m-3for the Tri-n-butyl phosphate at Resolute Bay land sampling, whereas it was only one ship sample result at a concentration of 100pg m-3 (Guo et al. 9). From the study’s findings, the halogenated concentrations were from river discharge that is Nelson and Churchill rivers. The non-halogenated organophosphate ester concentrations from the study findings are shown to have diffuse sources or local sources close to land-based sampling stations. There is increasing relevance of halogenated and no halogenated organophosphates esters contaminating the Arctic ocean from the results.

Human exposure

Due to the extended use of organophosphates by human beings, human beings are at the risk of higher exposure. Human beings gain exposure to the various organophosphates through various routes such as ingestion and inhalation of indoor dust as well as ingestion of contaminated food in the environment (Li et al. 35). The contaminated food can be through the fish they were caught from an organophosphate contaminated water source or through feeding of the improperly washed vegetables since the modern pesticides use organophosphates as active ingredients. The world health organization has approved the constitution of organophosphates to inflict significant health and environmental concern. Since there are no approved regulations, organophosphates use and human exposure increase, putting human beings at higher risks.

Similarities

Both Li and Shoaib reports indicate that the high exposure of human beings to organophosphates was attributed to the brominated flame retardants’ ban. From both studies, there have been increased exposure of the organophosphates’ human internal direction due to the widespread use of the organophosphates. Both studies objectively illustrate the various organophosphates in the environment and the route of exposure.

Differences

The study by Shoaieb was prompted by the insufficient information on the environmental organophosphate levels after the ban of the brominated retardants. Their study task is based on occurrence and dispersion of the 12 organophosphates in the urban setting. Their study involved several countries such as Canada, Turkey, and Egypt. Their research indicated a median organophosphate concentration for Vancouver in Canada to be 41.4 ug/g instead of those of Istanbul, Turkey, and Cairo, Egypt, which were low. From their findings, tris (2-butoxy ethyl) phosphate accounted for 56 and 92% concentration in Vancouver and Cairo, respectively, of all the total organophosphates esters. However, tris (2-butoxy ethyl) phosphate accounted for only 14% of the total organophosphates in Istanbul.  In Vancouver and Instabul, the findings indicated Tris (2-chlorophyll) phosphate to contain the most abundant chlorinated organophosphate esters at a 20 and 36% concentration, respectively, through the attention was too low to detect in Cairo dust samples. The findings’ overall results indicated estimated daily intakes of organophosphates from dust to be 115, 38, and 9ng/kg/BW/day for toddlers where the adult composition was ten times lower in the three countries understudy in the order; Vancouver, Cairo, and Istanbul. However, the total intake account for 115 to 2900, 38 to 845, and from 9-240 ng/kg BW/ day for the three countries respectively. TBOEP accounts for the largest portion of EDI among the toddlers and adults, while the toddler exposure indicating 4 to 80%, 2-44%, and 0.1-6% of the references doses for the toddlers above mean average intake in Vancouver, Cairo, and Istanbul.

The report by Li illustrates the various pretreatment protocols and instrumental analysis responsible for the occurrence of the organophosphate esters. Milk, hairs and nails make up the various human media which constitute of the organophosphates as well as mOPEs. The report further accounts for the health risks associated with the exposure and the challenges in the Organophosphates analysis, which is not expounded in the Shoaib study. United States account for the largest dialkyl and diaryl mOPEs as compared to Europe and Asia. Further, their reports projected tris (2-Chloroisoprophyl) phosphate, tris (1,3-dichroic-2-propyl) phosphate, and triphenyl phosphate to be the significant organophosphates originating the essential daily products. The study illustrates that human beings’ highest exposure to organophosphates occurs through ingestion rather than what Shoaib postulated to be dust. Organophosphates shorter biological lives and urine concentrations is an illustration of the long-term exposure which is attributed to the lower metabolic activities in the various conditions.

Recommendations for further research and action

Ultimately, there has been an increase in organophosphates’ accumulation in the environment due to the bromine retardants’ ban. The growth threatens human beings due to exposure in both outdoor and indoor as well as ingestion and inhalation. The various effluents of the organophosphates into the Water Rivers result from the increased release from the agricultural field and the use of organophosphate pesticides. Therefore, more is to be researched to expound on the reasons as to why the Organophosphates esters are cause for concern in modern society.

Works Cited

Blum, Behl, Birnbaum, Diamond, Phillips, Singla, & Venier. “Organophosphate ester flame retardants: are they a regrettable substitution for polybrominated diphenyl ethers?” Environmental science & technology letters, vol. 6, no. 11, 2019, pp. 638-649.

Ding, Han, Wu, Zhang, Li, Yu, & Mai. “Bioaccumulation and trophic transfer of organophosphate esters in a tropical marine food web, South China Sea.” Environment International, vol. 105919, no. 143, 2020.

Li, Zhao, Letcher, Zhang, Jian, Zhang, & Su. “A review on organophosphate ester (OPE) flame retardants and plasticizers in foodstuffs: levels, distribution, human dietary exposure, and future directions.” Environment international, vol. 127, 2019, pp. 35-51.

Nartop, Hasanoğlu Özkan, Yetim, & Sarı. “Qualitative enzymatic detection of organophosphate and carbamate insecticides.” Journal of Environmental Science and Health, Part B, vol. 55, no. 11, 2020, pp. 951-958.

Shoeib, Webster, Hassan, Tepe, Yalcin, Turgut, & Jantunen. “Organophosphate esters in house dust: A comparative study between Canada, Turkey and Egypt.” Science of the Total Environment, vol. 650, no. P1, 2019, pp.193-201.

Sühring, Diamond, Bernstein, Adams, Schuster, Fernie, & Jantunen. ” Organophosphate Esters in the Canadian Arctic Ocean.” Environmental science & technology, vol. 55, no. 1, 2020, pp. 127-153

Wang, Zhong, Xiao, Liu, Yang, Covaci, & Zhu. “Bioavailability and biomagnification of organophosphate esters in the food web of Taihu Lake, China.” Impacts of chemical properties and metabolism. Environment international, vol. 10, no. 125, 2019, pp. 25-32.

Wang, Li, Martínez-Moral, Sun, & Kannan. “Metabolites of organophosphate esters in urine from the United States.” Environment international, vol. 122, no. 6, 2019, pp. 213-221.