Although there are no other published studies on exposure specifically to CM alone, our data can be compared to previous studies of both non-occupational and occupational exposures to several pyrethroids. In comparing the urinary concentrations of the non-specific pyrethroid metabolite, 3-PBA, the Egyptian agriculture applicator’s peak urinary levels are about 50 times greater than the levels found in the 2010 US NHANES study of the general U.S. population in 2001–2002 . Hardt and Angerer assessed background excretion of urinary pyrethroid metabolites including DCCA from 45 urine samples in 25 women and men in Germany who had no occupational exposure to pesticides. The mean DCCA urinary concentration found in these samples was 0.8 g/g creatinine. The peak cis-DCCA concentrations in the Egyptian workers were more than 20 fold higher than the levels in this German population. Biological monitoring was carried outin a population of German agriculture workers involved in applications of various pyrethroid insecticides, including CM . The mean cis-DCCA and 3-PBA concentrations found in these workers were 0.6 and 1.8 g/g creatinine, respectively. These concentrations are also several fold lower than the peak levels observed in the Egyptian applicators.During the summer of 2008, the Egyptian workers applied the organophosphorus pesticide, chlorpyrifos,square black flower bucket to the cotton fields prior to the CM application. Farahat et al. estimated chlorpyrifos exposures in these workers using urinary TCPy as a biomarker for chlorpyrifos. During the chlorpyrifos application, Farahat et al. reported peak urinary TCPy levels on July 10 in field station 1 . This peak median urinary TCPy level corresponds to estimated internal chlorpyrifos dose of 578.4 g/kg/day.
The peak median CM doses estimated in the present study are several orders of magnitude lower than the estimated chlorpyrifos doses in this cohort. The route of exposure for chlorpyrifos in this occupational setting is primarily dermal and because the application method for both insecticides is the same , it is plausible that the primary route of exposure for aCM in this study is also dermal. Human dosing studies have shown that there are differences between the elimination half-life and the dermal adsorption for CPF and aCM. Griffin et al. and Meuling et al. both reported average CPF elimination half-lives of 41 h and ∼1% adsorption, based upon the recovery of the applied dose as urinary metabolites and the amount of chlorpyrifos recovered from the skin subtracted from the amount applied to the skin. Two human dosing studies with aCM and cypermethrin calculated an elimination half-life range of 8–22 h after the application of a single dermal dose, and ∼0.1% of the applied dose was recovered as urinary metabolite DCCA . The variance between the half-life and the absorption of CPF and aCM can explain, in part, why the levels of the aCM urinary metabolites cis-DCCA and 3-PBA did not reach the exceedingly high levels as seen for the CPF urinary metabolite TCPy. Several in vitro studies have shown that metabolism of pyrethroids is mediated by carboxylesterases . Crow et al., 2007 demonstrated that the activity of human carboxylesterase 1 and 2 is inhibited after treatment with chlorpyrifosoxon, the active metabolite of chlorpyrifos, and metabolism assays indicate that hydrolysis of trans-permethrin is inhibited by chlorpyrifos-oxon in human liver fractions .
The Egyptian agriculture workers were spraying chlorpyrifos for up to 17 days just prior to the application of CM on the cotton fields. Thus, there is potential for interactions in the metabolism of chlorpyrifos and CM in vivo. Prior exposure to chlorpyrifos could inhibit the carboxylesterases ability to detoxify CM, thereby altering the pharmacokinetic and toxic potential of CM. Future studies designed to assess the interactive effects of these two classes of insecticides will be critical in examining the impact of combined and sequential exposures on human health. Urinary cis-DCCA and 3-PBA concentrations were generally still elevated compared to baseline levels 7–11 days after the cessation of application . This result was unexpected based upon the reported mean urinary half-life of 13 h for aCM after a single dermal exposure . This finding may be explained by poor washing habits after handling the insecticide, continued exposure from wearing CM drenched clothing, or by workers re-entering the cotton fields and contacting CM residue on the cotton plants or in the soil. Another possible route of continued exposure is from skin or deep compartments such as fat tissue. CM is highly lipophilic and the internalized compound may get into skin layers where it is not readily removed by typical washing procedures , and fat compartments where it can be slowly released over time, metabolized, and excreted as urinary cis-DCCA and 3-PBA. Another explanation for the accumulation of urinary cis-DCCA and 3-PBA is the possibility that the pharmacokinetics of aCM metabolism and excretion in man are different from repeated and sustained exposure when compared to the single dermal dose that was used to estimate the half life range of 8–22 h .
Irrigation plays a key role in land surface fluxes and their interactions with atmospheric processes. Globally, it is estimated that the increase in water vapor fluxes from land due to irrigation is on the same order of magnitude as the decrease induced by deforestation . Irrigated systems have expanded in recent years to increase water use efficiency and crop productivity, yet expected water savings have led to greater water demands due to agricultural expansion . Nearly 10% of California’s land surface area is irrigated farmland, where high-revenue perennial crops account for about 40% of that land . Trends in the expansion of perennial crops as a replacement of annual crops are expected to result in a positive net surplus of water but will require policies and technologies to assure these benefits .California’s irrigated agriculture, and other semi-arid regions around the world, face growing threats by climate change, where an increase in precipitation variability is expected to result in more frequent, prolonged and extreme droughts . Regional climate models also project a challenging future related to natural water storage; by the end of this century water from snowmelt will occur 4 weeks earlier each year and also an expected 79% reduction in peak water volume would impact about 40% of California’s surface water storage . These water deficits are already being compensated for by increased reliance on groundwater to make up for surface water constraints, which is unsustainable at current rates of extraction . Continually improving our understanding of water use by high-value woody perennial crops will enable growers to improve the precision irrigation management needed to achieve sustainability goals. In California, woody-perennial crop water use needed for irrigation management is commonly based on some combination of direct soil moisture measurements and indirect crop evapotranspiration estimates. Actual ET is the effective water flux from the surface to the atmosphere due to soil evaporation and plant transpiration. Thus, the evapotranspiration flux derived through micrometeorological methods such as eddy covariance and surface renewal can be regarded as estimates of ETa. Three related concepts are potential evapotranspiration , reference crop evapotranspiration ,square black flower bucket wholesale and crop evapotranspiration . ETp represents an atmospheric water demand, thus the amount of water that can be transferred as water vapor to the air from the surface . ETo is commonly defined as the rate of evapotranspiration from a hypothetical crop with an assumed crop height and a fixed surface resistance and albedo , which would closely resemble evapotranspiration from an extensive surface of green grass cover of uniform height, actively growing, completely shading the ground and not short of water. ETc is usually regarded as the evapotranspiration from a given crop depending on plant growth and other surface characteristics, and thus is a function of a crop coefficient representing such crop/surface characteristics and ETo accounting for local weather conditions . ETo is commonly obtained from a nearby weather station and multiplied by a crop coefficient to obtain ETc. The use of any of these approaches can lead to crop water use estimates with a significant amount of uncertainty.
Such uncertainty is usually related to measurement quality and quantity, modeling assumptions, and logistical challenges of implementing these techniques in an operational context. While not absent of limitations and uncertainties, evapotranspiration fluxes derived through the eddy covariance technique can be considered as a direct measurement of crop water use. Moreover, eddy covariance flux measurements provide estimates at a temporal frequency that allows for the examination of sub-daily scale processes and relationships between different surface fluxes . The Grape Remote Sensing Atmospheric Profle and Evapotranspiration eXperiment project has collected micrometeorological and biophysical data in vineyards across two distinct California viticultural regions, North Coast and Central Valley, across several growing seasons. These regions not only exhibit different climatic conditions , but are also characterized by different grapevine varieties, canopy structure, management practices, and production goals that represent a wide range of conditions encountered by California wine grape growers. In this study, we capitalize the rich GRAPEX eddy covariance dataset to better understand wine grape water use across this range of conditions. GRAPEX aims to develop tools needed to remotely monitor ETa and inform optimal irrigation management for a given vineyard based on detailed information regarding ETa at high spatial and temporal resolutions . This study contributes to the overarching objectives of GRAPEX by exploring eddy covariance surface flux variability for five different vineyards and highlights the value of near-real-time actual evapotranspiration as part of new irrigation management tools. Daily, seasonal, and inter-seasonal surface flux patterns and relationships are investigated. ET patterns and variability are analyzed along with factors closely tied to vineyard management, namely vegetation density as expressed by leaf area index and water availability. LAI is related to vineyards phenology and influenced by vine training and pruning practices, as well as early-season irrigation, while water availability throughout the growing season is closely driven by irrigation practices.Micrometeorological flux measurements were collected over fve vineyards over the North Coast and Central Valley of California. According to the American Viticultural Areas boundaries, the three study sites where flux measurements were collected are located over the North Coast, Lodi, and Madera regions . In the North Coast region, there were two flux towers deployed at the North Coast study site: one in a Cabernet Sauvignon and another in a Petite Sirah vineyard. In the Lodi region, fluxes from a tower at the SLM study site in a Pinot Noir vineyard are presented for years 2018 and 2019, while in 2020 the block was converted to Cabernet Sauvignon by cutting the vines at the root stock and re-grafting the former variety. In the Madera region, there were flux towers deployed at the RIP study site over vineyards with varieties Merlot and Chardonnay. Additional details regarding location, wine grape variety, soil texture, canopy type, etc. for each experimental vineyard are presented in Table 1.Flux towers at each site were equipped with sensors to measure the main components of a surface energy balance , Sensible heat flux , Latent heat flux , and soil heat flux. Each tower had a very similar array of sensors, yet some differences were unavoidable due to the availability of sensors at the time of deployment and changes in technology throughout the deployment at the different study sites. A detailed list of the sensors deployed at each flux tower is presented in Table 2. The soil heat flux was calculated as the average of fve heat flux plates deployed along a diagonal transect across the inter-row space at a depth of 8 cm. At each soil heat flux plate location, soil thermocouples at depths of 2 cm and 6 cm, and a soil moisture sensor at a depth of 5 cm were installed.H and λE were computed as functions of 30-min average covariance of the corresponding variables sampled at 20 Hz. Anomalous records in the high-frequency time-series for each computed variable were removed following the Median Absolute Deviation method implemented by Mauder et al. . Wind velocity components were rotated into the mean stream wise flow following the 2-D coordinate rotation method described by Tanner and Thurtell , Kaimal and Finnigan , Foken and Napo . When necessary, wind velocity and the scalar quantities were adjusted in time to account for sensor displacement, and frequency response attenuation corrections were performed . Sonic temperatures were corrected based on Schotanus et al. , and the resulting fluxes were adjusted by the Webb, Pearman, and Leuning density corrections .