Imiprothrin was only detected in one of the urban homes which reported usage during the study; no other urban home had detectable imiprothrin levels indoors even though some of these households reported applying imiprothrin indoors prior to the study. Concentrations in samples collected 5-8 days apart in the same home were positively and significantly correlated for the most frequently detected analytes , except allethrin; Spearman rank-order correlation coefficients ranged from 0.70 to 1.00 .We detected several pesticides in most homes, including OP pesticides previously phased-out for residential uses, pyrethroids, and the pesticide synergist piperonyl butoxide . Biological exposure metrics for these pesticides are relatively transient and highly variable, typically reflecting recent exposures. However, consistent with other studies, we found that dust serves as a stable matrix and indicator of potential indoor exposure for some pesticides. The high correlations observed indust concentrations from samples collected 5-8 days apart suggests that, for some pesticides, measurements in house dust may be relatively stable indicators of potential indoor exposure over this time frame. To our knowledge, this is the first study to evaluate the correlation of concentrations within homes for several pesticides over a short sampling period. Although the detection frequency for chlorpyrifos and diazinon was higher in Salinas than Oakland, we did not observe statistically significant differences in pesticide concentrations or loadings between locations. This is notable given that >28,000 and 65,000 kgs of chlorpyrifos and diazinon, respectively, were applied for agricultural purposes in Monterey County in 2006 and minimal applications occurred in Alameda County. Previously, we showed a significant correlation with local agricultural use and chlorpyrifos dust concentrations for homes throughout the Salinas Valley. Mapping of dust concentrations and agricultural use suggests that chlorpyrifos dust concentrations are higher in the center of the Valley , container for growing weed where agricultural use is higher. farm worker homes in the present study were from the city of Salinas where the impact of drift from agricultural applications may have been lower.
Additionally, our small sample size may have prevented us from observing significant differences in concentrations between locations for these OP pesticides as well as other analytes. Malathion was not frequently detected in homes from either location; however, higher levels were observed in urban homes. This pesticide is used in agriculture and is also registered for use in home gardens, as a building perimeter treatment, as a wide-area spray for mosquitoes, and by prescription for head-lice control.However, no parents reported treating their children for lice or using it themselves in their gardens. The main county uses for this OP pesticide in 2006 in the urban region were landscape maintenance and structural pest control. These applications were reported more than 25 km away from the nearest study home, thus it is not readily apparent why higher levels were observed in urban homes although it should be noted that we only sampled a small number of homes. We generally observed significantly lower house dust concentrations of chlorpyrifos and diazinon in the present study compared to levels measured in dust from homes located in the same zip codes sampled between 2000 and 2002, suggesting that indoor concentrations in the city of Salinas are decreasing despite continued agricultural use in the area. In New York City, air concentrations for these OP pesticides in low-income homes also significantly decreased between 2001 and 2004. The temporal declines in indoor concentrations reported here and in the New York City study may reflect the decreasing usage of these OP pesticides for home or structural applications per the U.S. EPA’s residential phase-out. Nonetheless, despite declining concentrations indoors, detection of these OP pesticides, especially in Oakland where there was little agricultural or structural use, underscores their persistence indoors. Compared to other studies in farm worker populations , we observed lower median concentrations for chlorpyrifos and diazinon. These farm worker studies generally reported a wider range of concentrations for these two OP pesticides and collected dust samples prior to the residential phase-out. One study by Curl et al. reported a wider range of diazinon concentrations, but comparable median concentrations . Although malathion was not frequently detected in our farm worker homes, a wider range of concentrations was reported in previous farm worker studies. To our knowledge, only one other study has reported OP pesticide concentrations in low-income urban homes. This study reported higher median concentrations for chlorpyrifos and diazinon in low-income urban housing units in Boston, MA. Homes in this study were sampled just after or during the residential phase-out of chlorpyrifos and diazinon, respectively .
Similar to low-income urban housing units in Boston, MA, pyrethroids and PBO were detected in higher concentrations and used more frequently in our study homes compared to other pesticides. This finding is consistent with the fact that pyrethroid insecticide formulations for residential applications have largely replaced OP pesticide residential formulations. Although over 19,000 kgs of permethrin were applied in Monterey County in 2006 for agricultural purposes, we did not observe significant differences in permethrin concentrations between locations. Allethrin and cypermethrin were also widely detected in most homes. Our findings suggest that home use likely contributed to the presence of pyrethroid pesticides in house dust since pyrethroids were commonly used indoors and negligible to no agricultural applications took place at the county level . It is also possible that structural pest control applications influenced indoor detection of certain pyrethroids in some homes. For example, it is estimated that ~80% of the non-agricultural cypermethrin use reported in Alameda County in 2006 was for structural pest control. The presence of pyrethroids in house dust is also consistent with their physical and chemical properties, including high octanol:water partition coefficient values and low vapor pressures . To our knowledge, only two studies have measured pyrethroid dust concentrations in farm worker homes. Similar to the present study, permethrins were the most frequently detected pyrethroids indoors. Median cis- and transpermethrin concentrations in our farm worker homes were higher than those observed in a previous study. The detection of chlorthal-dimethyl in all Salinas farm worker homes and none of the Oakland urban homes is consistent with other Salinas Valley studies showing an association between agricultural use and house dust contamination and a positive correlation between outdoor and indoor air concentrations. This herbicide had relatively high agricultural use in the Salinas Valley and is not found in home-use pesticides. Chlorthal-dimethyl also has a high log Kow value and low vapor pressure , and may be bound to particulate matter at room temperature. Over 16,000 kgs of malathion and iprodione were used in 2006 for agricultural applications ; however, they were not commonly detected in farm worker homes from the city of Salinas. For some of these pesticides, e.g., iprodione, LODs were higher than for other analytes. Other factors including physicochemical properties, e.g., high vapor pressure and low log Kow values ,cannabis square pot may have resulted in lower detection frequencies.
These pesticides were also not frequently detected in dust samples from our previous study in the city of Salinas. This study has several limitations. Location differences in pesticide dust levels have been reported previously when using loadings rather than concentrations; however, our small sample size limits statistical power and may have prevented us from observing statistically significant differences between locations for concentrations and/or loadings. Additionally, although homes with insufficient sample mass were demographically similar to those with adequate sample mass, exclusion of these homes may have introduced some bias and prevented us from detecting a difference in pesticide concentrations and/or loadings between locations. We also focused on low-income homes and thus the results may not be generalizable to other populations. Although estimated intakes for select pesticides were below EPA RfDs , it should not be concluded that intakes below RfDs are “acceptable” or free of any health risks. For example, recent studies have identified mechanisms of OP pesticide toxicity that were not considered in defining current U.S. EPA RfDs. Moreover, RfDs do not account for differences in vulnerability to pesticide toxicity due to genetic factors, such as paraoxonase polymorphisms. Additionally, our intake calculations for pesticides do not account for other exposure pathways ; nor did we consider that some children could have pica or other behaviors that could increase or decrease intake. Although we surveyed participants on their usage of pesticides indoors, we were not always able to corroborate whether formulation ingredients were present at high concentrations as the pesticide containers were not always available to confirm the active ingredients. Lastly, children in the homes sampled are clearly exposed to multiple indoor contaminants and our hazard evaluation does not account for exposure to complex mixtures.The number of people with Parkinson’s disease has more than doubled in the past 30 years and, absent change, will double again by 2040. Numerous genetic causes or risk factors for the disease have been identified, but the vast majority of individuals with PD do not carry any of these mutations. Several environmental toxicants, especially certain pesticides, have also been linked to PD, and head trauma is also associated with an increased risk. However, these are insufficient to explain the widespread prevalence of PD. Given the disease’s growing rates—more than can be explained by aging alone—other less visible causes must be contributing to its rise. One of these may be trichloroethylene , a ubiquitous chemical that has contaminated countless sites and poses health risks to those who are exposed via their work or their environment.The evidence linking TCE to PD to date is based on a handful of case studie, a small epidemiological study linking exposure to a 500% increased risk of PD, and numerous animal studies demonstrating that the chemical leads to the pathological hallmarks of PD. Here we introduce the chemical, describe its association to PD and other diseases, detail its widespread use and routes of contamination, and provide circumstantial evidence for its broader role in PD through illustrative cases depicting individuals with the disease who were likely exposed to TCE through their environment or occupation. We conclude with a call for greater research on its effects on PD, protection from and remediation of contaminated sites, and banning of this century-old chemical that has caused immeasurable harm to the public’s health.TCE is a simple six-atom solvent that is clear, colorless, volatile, nonflammable, and environmentally persistent. It was first synthesized in the lab in 1864 , and commercial production began in the 1920s. Because of its unique properties, TCE has had countless industrial, commercial, military, and medical applications. Among these are producing other chlorinated compounds , cleaning electronics, and degreasing engine parts for civilian and military purposes. As it readily evaporates and does not shrink fabrics, TCE was used to dry clean clothes beginning in the 1930s. A closely related chemical called perchloroethylene , which has one additional chlorine atom in place of the hydrogen atom, largely supplanted TCE in dry cleaning in the 1950s. In anaerobic conditions, PCE often transforms into TCE, and their toxicity may be similar. TCE is found in numerous consumer products , including typewriter correction fluid, paint removers, and carpet cleaners. Until the 1970s, it was used to decaffeinate coffee. The volatile TCE was also an inhaled anesthetic until the U.S. Food and Drug Administration banned it in 1977.Studies linking TCE exposure to PD and parkinsonism date back to at least 1969 when Huber reported parkinsonism in a 59-year-old man who worked with TCE for over 30 years. Thirty years later, Guehl and colleagues documented PD in a 37-year-old woman who was exposed to the chemical while cleaning houses and again while working in the plastics industry. In 2008, Gash and colleagues reported that among 30 factory workers, three developed PD after using TCE for many years to degrease and clean metal parts. These three workers were stationed closest to an open TCE vat, and 14 of 27 workers who were further from the source “displayed many features of parkinsonism, including significant motor slowing”.Four years later, researchers found that in twin pairs, the twin with occupational or hobby exposure to TCE had a 500% increased risk of PD compared to their unexposed twin. Exposure to the closely related solvent PCE also trended toward significance with an odds ratio of 10.5. Notably, the researchers found an interval of 10 to 40 years from the time of TCE exposure to PD diagnosis.