Developing Effective Protocols to Protect Farmworkers from Heat Stress and Illness While Working in Polytunnels.

[Figure: see text]

Heat Stress: A Hazardous Occupational Risk for Vulnerable Workers

Organic vegetable farms on the Central Coast region of California are generally intensive operations. That is, two and sometimes three crops may be harvested off the same acreage each year. Many approaches exist for growing and marketing organic vegetables. This publication describes the range of soil management practices, pest management, crop rotations, cover crops, and harvest and packing methods currently used by organic growers on the Central Coast of California. Marketing options and state and federal regulations governing organic commodities are also discussed. A general sequence of operations, equipment requirements, resource use, costs, yield and return ranges are presented for thirteen vegetable crops and two cover crops. The vegetables included are cabbage, cauliflower, cucumbers, garlic, lettuce (leaf and romaine), onions (red and yellow), snap peas, snow peas, bell peppers (green and red), sweet corn, and winter squash (large and small varieties). Barley and vetch are the two cover crops detailed.

This year, the European Environment Agency published a report in which heat stress is defined as the most dangerous climate risk for the health sector. Society is expected to suffer from increasing heat stress events in the coming years. Moving towards impact-based forecasting, the Royal Netherlands Meteorological Institute (KNMI) has recently adopted the heat stress indicator Wet Bulb Globe Temperature (WBGT) as part of their Early Warning Centre.   The WBGT presented here is computed analytically from air temperature, relative humidity, wind speed and global radiation using the theoretical Liljegren approximation. These WBGT values are compared with WBGT values as derived from black bulb (globe) and air temperature observations for a specific station in the Netherlands.  We present a characterization of WBGT based on hourly observations made by Automatic Weather Stations (AWS) in the Netherlands and compare the safety levels as defined by the US Army, the world athletic organization and the Dutch fire brigade. By assessing the trends in WBGT over the past decades, we find a significant increase of hourly intervals where critical threshold values are exceeded for all five investigated stations. The safety levels of these organizations are based on the absolute values of WBGT. The effective WBGT (WBGTeff) also considers the effects of clothing and a person's activity. The total time in a day that the WBGTeff is above a certain threshold can therefore be used for warnings for specific work environments.   Looking into a case study of a Dutch triathlon (25 June 2023) with a combination of hot weather conditions which resulted in a high amount of heat strokes and hospitalizations, we show spatial variations of WBGT for that day using detailed maps based on AWS and crowd-sourced data.

There is considerable uncertainty regarding the impact of irrigation on heat stress, partly stemming from the choice of heat stress index. Moreover, existing simulations are at scales that cannot appropriately resolve population centres or clouds and thus the potential for human impacts. Using multi-year convection-permitting and urban-resolving regional climate simulations, we demonstrate that irrigation alleviates summertime heat stress across more than 1,600 urban clusters in North America. This holds true for most physiologically relevant heat stress indices. The impact of irrigation varies by climate zone, with more notable irrigation signals seen for arid urban clusters that are situated near heavily irrigated fields. Through a component attribution framework, we show that irrigation-induced changes in wet-bulb temperature, often used as a moist heat stress proxy in the geosciences, exhibit an opposite sign to the corresponding changes in wet bulb globe temperature—a more complete index for assessing both indoor and outdoor heat risk—across climate zones. In contrast, the local changes in both wet-bulb and wet bulb globe temperature due to urbanization have the same sign. Our results demonstrate a complex relationship between irrigation and heat stress, highlighting the importance of using appropriate heat stress indices when assessing the potential for population-scale human impacts.

In 2006, a deadly Escherichia coli O157:H7 outbreak in bagged spinach was traced to California's Central Coast region, where >70% of the salad vegetables sold in the United States are produced. Although no definitive cause for the outbreak could be determined, wildlife was implicated as a disease vector. Growers were subsequently pressured to minimize the intrusion of wildlife onto their farm fields by removing surrounding noncrop vegetation. How vegetation removal actually affects foodborne pathogens remains unknown, however. We combined a fine-scale land use map with three datasets comprising ∼250,000 enterohemorrhagic E. coli (EHEC), generic E. coli, and Salmonella tests in produce, irrigation water, and rodents to quantify whether seminatural vegetation surrounding farmland is associated with foodborne pathogen prevalence in California's Central Coast region. We found that EHEC in fresh produce increased by more than an order of magnitude from 2007 to 2013, despite extensive vegetation clearing at farm field margins. Furthermore, although EHEC prevalence in produce was highest on farms near areas suitable for livestock grazing, we found no evidence of increased EHEC, generic E. coli, or Salmonella near nongrazed, seminatural areas. Rather, pathogen prevalence increased the most on farms where noncrop vegetation was removed, calling into question reforms that promote vegetation removal to improve food safety. These results suggest a path forward for comanaging fresh produce farms for food safety and environmental quality, as federal food safety reforms spread across ∼4.5 M acres of US farmland.

Farmworkers in California’s Imperial Valley face a disproportionate risk of heat stress from prolonged exposure to extreme temperatures. However, heat stress is more than just extreme temperature and depends on humidity, winds, and sun exposure. These conditions can be aggregated into the wet-bulb globe temperature (WBGT), a metric endorsed by the U.S. Occupational Safety and Health Administration (OSHA) for monitoring workplace heat. To better inform heat mitigation strategies, we construct a climatology of summertime WBGT in Imperial Valley for 30 years during 1991–2020. The climatology is constructed from a dynamical downscaling of ERA5 reanalysis to 1.5 km using the Weather Research and Forecasting (WRF) Model, using quantile mapping to bias correct WBGT inputs against regional weather station observations. We find that WBGT is the highest in urban areas, where summertime daily maxima average 34°C and in rural croplands below mean sea level. National Weather Service (NWS) thresholds of WBGT that portend elevated heat stress are frequently exceeded, with 60%–70% of summer days exceeding the highest threshold of 32.2°C. WBGT also shows statistically significant warming trends over populated areas, and the onset of consecutive extreme WBGT days is occurring earlier in summer. Furthermore, breaks in the North American monsoon result in lower WBGTs, suggesting a source of intraseasonal WBGT predictability. These results underscore the need to downscale climate projections for the near future while bolstering heat mitigation and adaptation plans for vulnerable communities. Significance Statement Farmworkers in California’s Imperial Valley are at heightened risk of heat stress due to their prolonged heat exposure and unique social vulnerabilities. This heat stress can be proxied by the wet-bulb globe temperature (WBGT), which aggregates temperature, humidity, winds, and sun exposure. Using high-resolution climate modeling, we characterize summertime WBGTs in the Imperial Valley during 1991–2020. We find that the WBGT is the highest in urban areas and where croplands are below mean sea level. In fact, the average summertime WBGT is frequently above National Weather Service thresholds that indicate when rest periods should be taken. Furthermore, long-term warming trends and an earlier onset of extreme WBGT days put farmworkers increasingly at risk to heat stress. Additionally, we note that periods of relief from heat stress tend to occur during breaks in the North American monsoon, offering a route to improving forecasts of heat comfort. These results underscore the need for localized WBGT climate projections while bolstering heat mitigation and adaptation plans for vulnerable farmworkers.

Humid heat and associated heat stress have increased in frequency, intensity, and duration across the globe, particularly at lower latitudes. One of the more robust metrics for heat stress impacts on the human body is wet-bulb globe temperature (WBGT), because it incorporates temperature, humidity, wind speed, and solar radiation. WBGT can typically only be measured using nonstandard instrumentation (e.g., black globe thermometers). However, estimation formulas have been developed to calculate WBGT using standard surface meteorological variables. This study evaluates several WBGT estimation formulas for the southeastern United States using North Carolina Environment and Climate Observing Network (ECONet) and U.S. Military measurement campaign data as verification. The estimation algorithm with the smallest mean absolute error was subsequently chosen to evaluate summer WBGT trends and extremes at 39 ASOS stations with long continuous (1950–2023) data records. Trend results showed that summer WBGT has increased throughout much of the southeastern United States, with larger increases at night than during the day. Although there were some surprisingly large WBGT trends at higher elevation locations far from coastlines, the greatest increases were predominantly located in the Florida Peninsula and Louisiana. Increases in the intensity and frequency of extreme (90th percentile) WBGTs were particularly stark in large coastal urban centers (e.g., New Orleans, Tampa, and Miami). Some locations like New Orleans and Tampa have experienced more than two additional extreme heat stress days and nights per decade since 1950, with an exponential escalation in the number of extreme summer nights during the most recent decade. Significance Statement Humid heat and associated heat stress pose threats to health in the moist subtropical climate of the southeastern United States. Wet-bulb globe temperature (WBGT) is a robust metric for heat stress but must be estimated using complex algorithms. We first evaluated the accuracy of three WBGT algorithms in the southeastern United States, using measured verification data. Subsequently, we used the most accurate algorithm to investigate WBGT trends and extremes since 1950 in 39 cities. Results showed that summer heat stress has increased throughout the region, especially at night. Increases in the intensity and frequency of extreme heat stress were most prevalent at urban coastal locations in Florida and Louisiana, emphasizing the impacts of increased urbanization and evaporation on heat stress.

Heat stress has been implicated as a risk factor for cardiovascular disease (CVD). Wet bulb globe temperature (WBGT) is considered a more physiologically relevant measure of heat stress than temperature alone, accounting for direct sunlight, relative humidity, solar radiation, and wind speed. Pregnant individuals may be particularly vulnerable to heat stress due to physiological changes in thermoregulation. Pregnancy may serve as a sensitive period influencing future health, but it is unknown if prenatal heat stress impacts postpartum cardiovascular health. We examined associations between prenatal, residential WBGT exposure and postpartum Pathobiologic Determinants of Atherosclerosis in Youth (PDAY) risk scores, which predict future atherosclerosis. Among 193 participants from the Maternal and Developmental Risks from Environmental and Social Stressors pregnancy cohort, annual postpartum PDAY scores were calculated across 6 years postpartum, using age, non-high-density lipoprotein cholesterol, high-density lipoprotein cholesterol, hypertension, obesity, and hyperglycemia from in-person questionnaires and biomarker samples. We used hierarchical generalized additive models (GAMs) to examine associations between pregnancy average and trimester-specific WBGT and postpartum PDAY scores. Effect modification by prenatal psychosocial stressors, urban heat island index (UHII), and climate vulnerability index (CVI) was assessed through stratification. Distributed lag non-linear models (DLNM) with mixed effects assessed weekly associations. Models were adjusted for maternal age at consent, pre-pregnancy body mass index, household income, maternal education, race/ethnicity, and conception season. Model fit indices indicated a nonlinear relationship between average prenatal WBGT and postpartum PDAY scores, with a positive association emerging at temperatures above 19°C, though confidence intervals were wide. We were unable to observe evidence of associations with trimester-specific WBGT, sensitive windows of exposure, or effect modification by psychosocial stressors, UHII, or CVI. Our data suggested an association at pregnancy average WBGT greater than 19°C with postpartum cardiometabolic health risk scores, however sparsity at temperature extremes limited our conclusions. The relatively limited exposure variability in our study region and small sample size may have limited our ability to observe more robust associations.

IntroductionFarmworkers are at risk of heat related illness (HRI). The main contributors are thought to be environmental temperatures and activity levels, but the association has not been objectively assessed.MethodsCalifornia farmworkers...

Heat stroke cases during pre-season football practice are an annual rite of summer in the United States. Previous work (Kulka, T. J., and W.L Kenney. Heat Balance Limits in Football Uniforms. Phys. Sportsmed. 30:29–39, 2002) examined esophageal temperature during treadmill walking in an environmental chamber at 35% of VO2 max. Subjects wore a full football uniform or a full football uniform with shorts instead of padded pants. Results were expressed as a series of dry bulb temperatures (T) and associated relative humidities (RH) at which the exercising subjects could no longer maintain thermal balance. Translation of these limiting conditions into Wet Bulb Globe Temperature (WBGT) could help to standardize environmental guidelines for football. PURPOSE To express these uncompensable environmental conditions as WBGT. METHODS The exercise study graphs were digitally sampled to provide data points. Each uncompensable pair of T and RH was used to calculate an equivalent wet bulb temperature (WB). A general relationship between black globe temperature (GT) and T was calculated using summertime data from a grassy field and from a grandstand. 7266 pairs of GT and T were utilized, with the relationship between GT and T being GT = 0.9411T+23.665 (r = 0.69, mean error = 0 ± 6.7°F). [In °C, GT = 0.9411T + 12.1]. A GT was then calculated for each exercise study T, and each set of WB, GT and T values was used to calculate a WBGT for each data point using the formula WBGT = 0.7WB+0.2GT+0.1T. RESULTS WBGT limits for uncompensable heat stress were as follows: Full uniform 76.5 to 83.1°F (24.7–28.4°C); partial uniform 82.4–85.2°F (28–29.6°C); T-shirt and shorts 88.8–91.5°F (31.6–33.1°C). (These values are stated as ranges due to interactions between T and RH.) CONCLUSION These findings suggest that exercise in a football uniform can lead to uncompensable heat stress in conditions commonly found in late summer in the US. Use of a WBGT monitoring instrument could provide a convenient method for adjusting football workout protocol in light of practice field environmental conditions.

The purpose of this study was to investigate which climate/heat indices perform best in predicting heat-induced loss of physical work capacity (PWCloss). Integrating data from earlier studies, data from 982 exposures (75 conditions) exercising at a fixed cardiovascular load of 130 beats·min-1, in varying temperatures (15-50°C), humidities (20-80%), solar radiation (0-800 W·m-2), wind (0.2-3.5 m·s-1), and two clothing levels, were used to model the predictive power of ambient temperature, universal thermal climate index (UTCI), wet bulb globe temperature (WBGT), modified physiologically equivalent temperature (mPET), heat index, apparent temperature (AT), and wet bulb temperature (Twb) for the calculation of PWCloss, skin temperature (Tskin) and core-to-skin temperature gradient, and thermal perception (thermal sensation vote, TSV) in the heat. R2, RMSE, and Akaike information criterion were used indicating model performance. Indices not including wind/radiation in their calculation (Ta, heat index, AT, and Twb) struggled to provide consistent predictions across variables. For PWCloss and TSV, UTCI and WBGT had the highest predictive power. For Tskin, and core-to-skin temperature gradient, the physiological models UTCI and mPET worked best in seminude conditions, but clothed, AT, WBGT, and UTCI worked best. For all index predictions, Ta, vapor pressure, and Twb were shown to be the worst heat strain predictors. Although UTCI and WBGT had similar model performance using the full dataset, WBGT did not work appropriately in windy, hot-dry, conditions where WBGT predicted lower strain due to wind, whereas the empirical data, UTCI and mPET indicated that wind in fact increased the overall level of thermal strain. The findings of the current study highlight the advantages of using a physiological model-based index like UTCI when evaluating heat stress in dynamic thermal environments.NEW & NOTEWORTHY There is an urgent need to determine the optimal heat stress metric when forecasting the impact of heat stress on human performance, physiological stress, and perception. We analyzed a wealth of laboratory data, simulating heart rate (HR)-paced work with wide variations in air temperature, humidity, wind speed, solar radiation, and clothing. We conclude that the universal thermal climate index (UTCI) [followed by wet-bulb globe temperature (WBGT)] is the optimal heat index to reliably predict reductions in performance, and elevations in physiological and perceptual stress.

Introduction: One of the few certain impacts of climate change is the increase in the heat stress exposure. Heat exposure in the working environment is an important factor of occupational health. Among various heat indices, Wet Bulb Globe Temperature (WBGT) is a well-established measure of occupational heat stress, health and work capacity. It is a linear combination of four environmental factors namely temperature, humidity, wind speed and radiation. In this work, we examined the changes in WBGT under the climate change scenario over India for the period 1975-2100. Methodology: RegCM4.3 model outputs of meteorological parameters are analyzed to calculate the WBGT (indoor). The biases in the model simulations are corrected first for the historical period (1975-2004) with respect to Indian Metrological Department data and MERRA reanalysis data using the technique of linear regression. For the future, projected outputs from RegCM are analyzed for RCP4.5 and RCP8.5 scenarios. WBGT range is subdivided into five risk levels using comfort classes (Balazejezyk et al., 2011) as comfort (WBGT<WBGT<WBGT<WBGT30). The analysis and interpretation are carried out in view of the seven surface temperature homogeneous zones of India to understand the impact of climate change on heat stress exposure. Results: Spatial mapping for the entire country was carried out using GIS to identify the hotspots. In the last three decades, 21%, 33%, 34% 10% and 2% of the days annually correspond to 'comfort', 'warm', 'hot', 'very hot' and 'sweltering' conditions. The relative occurrences of the various comfort classes show large heterogeneity in space and time. The changes in the future for different 'climate change' scenarios are also quantified. Discussions: This study is a first attempt to assess the impact of climate change on heat stress and the implication for occupational health and productivity loss for the entire country.

BackgroundThe present study aimed at demonstrating the heat stress situation (distribution and intensity) based on a standard and common heat stress index, Wet Bulb Globe Temperature (WBGT), during hot seasons and interpret the obtained results considering global warming and rising temperature in different parts of the country based on climate changes studied in Iran.MethodsHeat stress assessment was done using WBGT index. Environmental parameters were measured simultaneously in the early, middle and end of shift work. The personal parameters including cloth thermal insulation and metabolic rate of 242 participants from 9 climatic categories were recorded for estimating effective WBGT (measured WBGT plus cloth adjustment factor as well as metabolic rate effect). The values of the indicator were categorized in the statistical software media and then linked to the climatic zoning of the data in the GIS information layers, in which, WBGT values relating to selected stations were given generalization to similar climatic regionalization.ResultsThe obtained results showed that in the summer about 60 % and more than 75 % of the measurements relating to 12 pm and 3 pm, respectively, were in heat stress situations (i.e. the average amount of heat stress index was higher than 28 °C). These values were found to be about 20–25 % in the spring. Moreover, only in the early hours of shift work in spring could safe conditions be seen throughout the country. This situation gradually decreased in the middle of the day hours and was replaced by the warning status and stress. And finally, in the final hours of shift work thermal stresses reached their peaks. These conditions for the summer were worse.ConclusionsRegarding several studies related to climate change in Iran and the results of present study, heat stress, especially in the central and southern parts of Iran, can be exacerbated in the decades to come if climate change and rising temperature occurs. Therefore, paying attention to this critical issue and adopting macro-management policies and programs in the field of workplace health is essential.

Heat Stress in the Workplace