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Risk assessment of OP pesticides requires knowledge of the magnitude of the exposure

It has been shown that a semivolatile pesticide such as chlorpyrifos can volatilize days after its indoor application and can be adsorbed to various surfaces . Children’s felt toys, in particular, and, to a lesser extent, plastic toys accumulated significant levels of chlorpyrifos. For a young child exhibiting typical mouthing and hand-to-mouth behavior, dermal and nondietary oral exposure to such conditions were estimated to constitute a dose of 64 µg/ kg/d under the most conservative absorption assumptions and to contribute between 40 and 60% of the total dose. This greatly exceeds the allowable daily intake of 10 µg/kg/d proposed by the US EPA.Therefore, either environmental or biological monitoring is used. In recent years, environmental monitoring has yielded information on concentrations of OP pesticides in outdoor, indoor, and personal air; indoor dust; soil; and foods and beverages . All of the measured values vary considerably, but it is difficult to determine whether they reflect mostly methodological differences or represent true differences in pesticide concentrations. Note that many of the available studies have focused on chlorpyrifos and diazinon. The US EPA eliminated essentially all indoor residential uses of these pesticides by 2002, but they continue to be used in agriculture. Several important findings have emerged from these exposure assessment studies. OP pesticides are detectable in essentially all media analyzed, including food, indoor air, dust, and soil near the home. Interestingly, OP pesticides were not detected in duplicate beverage samples in two studies , whereas others reported their detection in 4 of 21 beverage samples; 4 of 9 of the samples that included apple juice contained azinphosmethyl . Comparisons of pesticide concentrations in dust, soil,cannabis curing and surface and hand wipes have clearly indicated that exposure of agricultural families is considerably greater than that of non-agricultural reference families . This higher exposure appears to result from both take-home pathways and proximity of the residence to farmland , although the association with proximity is not a consistent finding .

Using food consumption data from the Nurses Health Study and the Health Professionals’ Follow-Up Study combined with the data from the Food and Drug Administration Total Diet Study, researchers estimated that mean daily dietary intakes of chlorpyrifos, diazinon, and malathion were 0.8, 0.5, and 5.5 µg/d for women and 0.9, 0.5, and 6.1 µg/d for men, respectively . From duplicate diet samples, adult dietary chlorpyrifos and malathion exposure has been estimated to be 0.5 and 1.3 µg/d, respectively , and dietary chlorpyrifos intake in children was estimated to be 0.263 µg/d . Mean aggregate chlorpyrifos exposure from a total of six pathways was calculated to be 1.39 µg/d ; inhalation made the greatest contribution , whereas only between 7 and 13% was attributable to pesticide residues in solid food, and the dermal route was negligible . In two studies of children’s pesticide exposure, however, solid food made the greatest contribution to the cumulative intake of chlorpyrifos, malathion, and diazinon . Interestingly, despite the high contribution that food appeared to make to aggregate chlorpyrifos exposure in the Minnesota Children’s Pesticide Exposure Study, there was a much stronger correlation between urinary metabolites of this pesticide and concentrations in personal air than with levels in the ingested solid food . Additionally, note that the estimates of dermal absorption neglected to account for the volatilized portion of chlorpyrifos. The finding of a high correlation between chlorpyrifos in indoor air and in the corresponding dermal wipes suggests that this route of exposure may be important . The reported dietary pesticide intakes were generally well within the US EPA or similar reference values . However, it has been noted that dietary intake estimates greatly depend on the assumed value of nondetect samples, with assumption of a zero value underestimating exposure by a factor of 10 to 60 . Bio-monitoring of OP pesticide exposure most commonly involves measurement of their urinary metabolites or, much more rarely,quantification of the pesticides themselves and/or some of their metabolites in plasma .

Whereas urinary dialkylphosphate metabolites are nonspecific because they can be derived from a wide variety of OP compounds, certain other urinary metabolites are specific for one or two pesticides . Recall that urinary metabolites of OP pesticides can provide only rough estimates of exposure because the amount of absorption and the fractional excretion of specific metabolites are not really known, nor have all the metabolites been identified. Additionally, it cannot be determined whether and to what extent urinary metabolites represent exposure to one or more parent compounds or direct exposure to their metabolites. Furthermore, urinary metabolite concentrations should be corrected for dilution, but the appropriate method is still under debate , particularly because marked seasonal fluctuations in creatinine levels were observed in small children . Bio-monitoring of prenatal exposure involves the measurement of pesticides and their metabolites in umbilical cord blood, amniotic fluid, or meconium. A total of eight pesticides were detectable in 45 to 77% of maternal plasma samples obtained at delivery and in a similar percentage of cord plasma samples from 230 mother–infant pairs from New York City . Their concentrations in maternal and cord plasma were similar and highly correlated, indicating the occurrence of transplacental transfer and substantial in utero exposure . A further indication for transplacental transfer comes from the finding that the DAP metabolites DEP, dimethyl phosphate, and dimethylthiophosphate were detected in 10, 10, and 5% of amniotic fluid samples, respectively . Meconium consists of fetal bile secretions along with the content of the amniotic fluid that the fetus swallowed, representing exposure from the second trimester through delivery, and is usually not excreted by the fetus until after birth. DEP and diethylthiophosphate were present in 95 and 100% of 20 meconium samples from New York newborns, respectively, whereas other OP metabolites were detected in only one or none of the samples . Similarly, the detection of diazinon , malathion , parathion , and chlorpyrifos , along with various organochlorine compounds, has been reported in meconium samples from infants in the Philippines . Up to six or seven pesticides were detected in 4 and 5% of the samples, respectively. Some investigators detected an association between reported indoor residential pesticide use and urinary concentrations of specific pesticide metabolites, but this association was not detected in several other studies of children and adults . Reported pesticide use in the garden is also not consistently associated with urinary DAP levels .

A significant correlation was reported between levels of chlorpyrifos, diazinon, and the carbamate propoxur in personal air and the concentrations of these insecticides or their metabolites in plasma obtained within a month of the personal monitoring, but there was no correlation in plasma obtained at later time-points . Because of the relatively short half-lives of these pesticides, the relevance of these correlations is difficult to evaluate without further information about the regularity or chronicity with which the women were exposed to these pesticides. Several studies in which urinary pesticide metabolite levels were measured have confirmed the findings of environmental monitoring studies that farm children are exposed to higher levels of OP pesticides compared with children from non-agricultural reference families ,drying weed particularly during periods of pesticide application . In one of these studies, azinphosmethyl was the pesticide detected with the highest frequency and at the highest concentrations in house dust and was significantly correlated with dimethyl DAP metabolites in urine . Only the study that detectedan association between house dust levels of azinphosmethyl and phosmet and proximity to farmland also found higher dimethyl DAP levels in children living near treated orchards compared to those living at a greater distance . In the same group of subjects, however, urinary levels of the major chlorpyrifos metabolite, 3,5,6-trichloro-2-pyridinol were not significantly different between children from agricultural and non-agricultural families and did not reflect distance from orchards, although chlorpyrifos was present at higher concentrations in house dust of farming families and was increased with increasing distance from pesticide-treated areas . Although studies of exposure to individual pesticides, even those considering aggregate exposure, have generally found the estimated exposure levels to be well below the RfD , there is increasing evidence from biological monitoring studies that exposure to OP pesticides overall may exceed reference doses in a substantial number of subjects from both agricultural and non-agricultural areas. Calculations of exposure using urinary DAP metabolites are difficult because these metabolites can originate from a large variety of OP pesticides with highly different chronic toxicity and RfD values. In 2- to 5-yr-old children from urban and suburban areas of Seattle, the percentage of exposure estimates exceeding US EPA guidelines ranged between 0 and 100%, depending on which pesticide was assumed to be responsible for the exposure . When pesticides commonly applied in an agricultural community in Washington were used to calculate the absorbed daily dose in children age 6 yr or younger, 9 to 56% of children from agricultural families and 0 to 44% of reference children exceeded the EPA RfD for azinphosmethyl and phosmet during the spray season . Similar calculations for the same age groups of children from Yuma County, Arizona, indicated that the highest daily dose values were 61 to 385 times higher than the EPA RfD . In a study of pregnant women in the Salinas Valley in California, the estimated exposure to OP pesticides exceeded the oral benchmark dose10 of the US EPA in 0 to 36% of the women, depending on the index chemical on which the estimate was based and exceeded the benchmark dose for 10% response in approx 15% of women regardless of the parent compound .

The benchmark doses for 10% response are doses expected to result in a 10% reduction in brain cholinesterase activity in rats. Notably, there is evidence from urinary DAP assessments that suggests that consumption of a predominantly organic diet can greatly reduce dietary exposure to OP pesticides as well as the associated risk . However, daily consumption of a single meal prepared with organically grown produce was not sufficient to significantly influence urinary levels of DAP metabolites .OP pesticides and carbamates inhibit acetylcholinesterase . Because AChE inactivates acetylcholine at neuronal junctions, its inhibition results in ACh accumulation and continued neurotransmission. Because the autonomic, the somatic, and the central nervous systems all use ACh, the symptoms of OP-mediated AChE inhibition are manifold and include dizziness, headache, confusion, convulsions, blurred vision, respiratory distress, bradycardia and hypotension, fatigue, weakness, ataxia, muscle cramps, and increased lacrimation and salivation. Although the effects of environmental OP exposure are milder, they can resemble those of acute poisoning and, incidentally, include some well-known SBS symptoms, such as tearing eyes, chest pressure/tightness, and feeling dazed . Numerous animal studies have documented the developmental neurotoxicity of gestational or early postnatal exposure to OP pesticides at relatively low levels that did not result in overt systemic toxicity and inhibited cholinesterase to a minor extent in the dam. Such exposure resulted in impairments in maze performance, locomotion, coordination and balance, righting reflexes, and cliff avoidance. The molecular and cellular changes in the fetal or newborn brain that could account for these effects include inhibition of brain AChE and choline acetyltransferase activity , alteration of muscarinic receptor function via inhibition of ligand binding and permanent reduction in the density of muscarinic cholinergic receptors , altered synaptic development and function that can persist into adulthood , decreased expression and activity of multiple components of the adenylyl cyclase cascade , impaired DNA and RNA synthesis , and reduced cellularity and brain weight in offspring. Most of these studies were performed using chlorpyrifos, but similar effects and mechanisms were observed with other OP pesticides as well as two different pyrethroids . Few studies have addressed possible neurodevelopmental effects of prenatal OP exposure in humans. Recently, the association between prenatal OP pesticide exposure and neonatal neurodevelopment as assessed by the Brazelton Neonatal Behavioral Assessment Scale was investigated in 381 full-term infants in the CHAMACOS project. Table 11 includes maternal DAP metabolite levels during pregnancy in this cohort of women, which contained a substantial portion of agricultural workers from the Salinas Valley and other women with rather high environmental exposure to pesticides because of their heavy use in this agricultural center.

Participants reported relative stress during SIP compared to their own previous stress level

Gulbas and colleagues identify a series of factors relevant to both NSSI and suicide that correspond to features we found among the SWYEPT participants, including family fragmentation, conflict, physical and sexual abuse, and domestic violence. The relationships among these factors are complex and are found cross-culturally, though they tend to be more severe with suicide than with NSSI . Logistic regressions examined differences by mid-SIP PA in likelihood of increased stress at mid-SIP and use of each stress management strategy at mid-SIP, adjusting for age, race, education, income, employment, and past-month alcohol use . Chisquare tests examined the association between mid-SIP stress and PA pattern, and between midSIP stress and mid-SIP use of stress management strategies. P-values < 0.05 were considered statistically significant. Managing stress while complying with the uniquely disruptive COVID-19 SIP restrictions may require a variety of stress management strategies. In a sample of adults mostly residing in Northern California, we examined relationships between stress, physical activity, and other stress management strategies during SIP. Participants who were physically active during SIP were less likely to feel increased stress during SIP and were more likely to report use of physically active stress management strategies. Additionally, physically active participants were less likely to report managing stress by sleeping more or eating more. Participants who reported managing stress using outdoor PA, indoor PA, and reading were less likely to feel increased stress during SIP. Those who managed stress by watching TV/movies, sleeping more, and eating more were more likely to feel increased stress. The association between greater PA and lower stress was consistent with hypotheses and with the extensive literature on the positive effects of PA on stress reduction in non-COVID contexts .

Engaging in PA may have significantly reduced stress incurred by COVID-19. Alternatively, participants with fewer stressors may have found it easier to be physically active. In this study, vertical farming systems cost participants meeting PA guidelines were older, more likely to be White and to drink alcohol, had greater educational attainment and higher household income, and were less likely to be employed . These participants may represent a subset of adults with greater resources and fewer demands on their time during SIP, leading to lower stress and increased ability to engage in PA. Nonetheless, the association between PA and stress remained statistically significant after accounting for age, race, past-month alcohol use, education, household income, and employment status. Engaging in PA may have contributed to stress management, even for participants who already had many advantages. This study suggests that the well-documented positive effects of PA on stress management persist even in the highly unusual circumstances of SIP. Active and less active participants also differed in the stress management strategies they employed. A majority of active participants reported that they used PA—especially outdoor PA — to manage stress. Active participants were four times more likely than less active participants to report managing stress using outdoor PA than inactive participants. Active participants were also more likely to report use of indoor PA, yoga, meditation, or prayer, gardening, and reading. Most of these activities involve a physical activity component. Additionally, physically active participants were less likely to cope with stress by eating more or sleeping more. Disruptions in diet are common during stressful times. Similar to the present study, a study of Belgian university students found students with more stress and less physical activity were at greatest risk for increased snacking during a stressful final exam period . COVID-19 SIP is a more widespread, disruptive, long-term stressful circumstance than a final exam period, yet similar results were found. Sleep disruptions have also been linked to stress during COVID-19 self-isolation . Indeed, in the current study, participants who managed stress by eating more, sleeping more, or watching TV/movies were more likely to report increased stress. Eating, sleeping, and watching TV/movies may have been used to manage stress by participants who were already experiencing a great deal of stress.

These activities require less energy to initiate than the more active strategies and may have felt more manageable. Concurrently, these less active strategies may have been less effective than strategies involving physical activity. Participants who coped with stress using PA or reading were less likely to report increased stress. Making PA—especially outdoor PA— more accessible during COVID-19 SIP may help ease stress. Recent changes in SIP policies in the San Francisco Bay Area have opened up local parks and activity areas . Overall level of PA during SIP, rather than change in PA, was associated with stress. Specifically, participants who became active or became less active during SIP did not significantly differ in likelihood of increased stress from those who were active throughout SIP. On the other hand, those who were less active both before and during SIP were more likely to experience increased stress. Low physical activity may be associated with other risk factors for stress, such as long work hours, that persisted during SIP. The study period was short and may not have been sufficient to show long-term associations. Other research has found that improvement in stress management over time is associated with increases in PA . As people adjust to COVID-19 and its associated restrictions, stress management and PA may improve. Although PA remained fairly consistent over the one-month study period , the proportion of participants reporting increased stress during SIP decreased substantially . Engaging in PA throughout SIP may further decrease stress. Stress management is crucial during COVID-19, as stress can increase susceptibility to viral infection . This study was observational and precludes causal conclusions about the role of PA in reducing stress. Analyses adjusted for numerous potential confounding factors; however, analyses were correlational. Generalizability of results is limited due to the non-representative sample. Most participants resided in Northern California, where the weather is generally conducive to outdoor PA year-round. The sample was predominantly middle-aged, female, White or Asian, and highly educated, with high household incomes. Although PA has near universal benefits, disparities in the ability to engage in PA during COVID-19 are likely. To our knowledge, such disparities have not yet been studied. Future research is needed to examine the role of PA in COVID-19 stress management among more socio-demographically and geographically diverse populations.

Participants were surveyed at the beginning of SIP and one month into SIP. Longer follow-up may show different patterns of results. The measure of stress used in this study was designed to capture changes in stress specific to SIP in a single item, with high face validity. Validated measures of stress, while less specific to SIP, should be used in future longitudinal research to expand upon the present study. Copper is toxic to life at levels that vary depending on the organism. Humans are mandated to not exceed 1–2 mg/L copper in their drinking water , while some freshwater animals and plants experience acute toxic effects at concentrations as low as 10 µg/L . Because the human food chain begins with plants, it is critical to understand how plants tolerate heavy metals including copper, which is frequently concentrated in soils as a result of pesticide application, sewage sludge deposition, mining, smeltering, and industrial activities. This issue is also at the crux of applying phytoremediation approaches, which use green plants to decontaminate or contain polluted soils and sediments and to purify waste waters and landfill leachates . Metal-tolerant plants inhibit incorporation of excess metal into photosynthetic tissue by restricting transport across the root endodermis and by storage in the root cortex . In contrast, hyperaccumulating plants extract metals from soils and concentrate excess amounts in harvestable parts such as leaves. Copper detoxification seems to be linked to mechanisms that bind Cu to molecular thiol groups. Cysteine-rich peptides, such as phytochelatins which transport copper to the shoot, increase in response to high cellular levels of Cu , and Cu-S binding occurs in roots and leaves of Larrea tridentata. However,vertical farming towers racks an unidentified copper species, concentrated in electron-dense granules on cell walls and some vacuole membranes, appears to be the main morphological form of copper sequestered in Oryza sativa , Cannabis sativa , Allium sativum , and Astragalus sinicus . Plants take in and exclude elements largely at the soil-root interface within the rhizosphere, i.e. the volume of soil influenced by roots, mycorrhizal fungi, and bacterial communities . Deciphering processes that control the bio-availability of metals in the field is difficult because the rhizosphere is compositionally and structurally complex. Here we report on using synchrotron-based microanalytical and imaging tools to resolve processes by which metal tolerant plants defend themselves against excess cationic copper. We have mapped the distribution of copper in self-standing thin sections of unperturbed soils using micro-Xray fluorescence and identified structural forms of copper at points-of-interest using micro-extended X-ray absorption fine structure spectroscopy and X-ray diffraction . Because only a few small areas could be analyzed in reasonable times with microanalyses, the uniqueness of the microanalytical results was tested by recording the bulk EXAFS spectrum from a sample representing the entire rhizosphere and by simulating this spectrum by linear combination of copper species spectra from POIs. We investigated copper speciation in rhizospheres of Phragmites australisand Iris pseudoacorus, two widespread wetland species with high tolerances to heavy metals .P. australisis frequently used to treat waste waters because it can store heavy metals as weakly soluble or insoluble forms. Its roots can be enriched in Cu 5-60 times relative to leaves, with large differences among ecotypes and between field-grown versus hydroponically grown plants . To take into account natural complexity, including any influence of bacteria, fungi, or climate variation, our experiment was conducted outdoors, rather than in a greenhouse on seedlings using ex-solum pots or hydroponic growth methods.

The soil was from the Pierrelaye plain, a 1200 ha truck-farming area about 30 km northwest of Paris, France. From 1899 to 1999, regular irrigation of the Pierrelaye plain with untreated sewage water from Paris caused contamination with heavy metals, mainly Zn, Pb, and Cu . Such pollution is pervasive worldwide because increasing populations and associated economic growth are diminishing available freshwater, thus leading to increased irrigation of farmlands with waste waters.In the initial soil, copper occurs in two morphological forms . One form decorates coarse organic particles that have some recognizable structures from reticular tissue , and the other occurs inThe rhizospheres were oxidizing as indicated by the presence of iron oxyhydroxide , absence of sulfide minerals, and the fact that P. australis and I. pseudoacorus are typical wetlands plants with aerenchyma that facilitate oxygen flflow from leaves to roots . Thermodynamic calculations using compositions of soil solutions collected below the rhizosphere indicate that Cu+ and Cu2+ species should have been dominant . These points along with the occurrences of nanocrystalline Cu0 in plant cortical cells and as stringer morphologies outside the roots together suggest that copper was reduced biotically. Ecosystem ecology of the rhizosphere indicates synergistic or multiple reactions by three types of organisms: plants, endomycorrhizal fungi, and bacteria. Normally, organisms maintain copper homeostasis through cation binding to bioactive molecules such as proteins and peptides. When bound, the Cu2+/Cu1+ redox couple has elevated half-cell potentials that facilitate reactions in the electron-transport chain. Even though average healthy cell environments are sufficiently reducing , there are enough binding sites to maintain copper in its two oxidized states. Copper is also important in controlling cell-damaging free radicals produced at the end of the electron-transport chain, for example in the superoxide dismutase enzyme Cu-Zn-SOD, which accelerates the disproportionation of superoxide to O2 and hydrogen peroxide. However, unbound copper ions can catalyze the decomposition of hydrogen peroxide to water and more free radical species. To combat toxic copper and free radicals, many organisms overproduce enzymes such as catalase, chelates such as glutathione, and antioxidants . Mineralization could also be a defense against toxic copper, but reports of Cu+ and Cu2+ biominerals are rare; only copper sulfide in yeast and copper oxalate in lichens and fungi are known. Atacamite 3Cl in worms does not appear to result from a biochemical defense. Biomineralization of copper metal may have occurred by a mechanism analogous to processes for metallic nanoparticle synthesis that exploit ligand properties of organic molecules. In these processes, organic molecules are used as templates to control the shape and size of metallic nanoparticles formed by adding strong reductants to bound cations. For copper nanoparticles and nanowires, a milder reductantsascorbic acidshas been used.