A comprehensive evaluation of heat stress and heat strain in a sample of sugarcane cutters in Brazil

Sugarcane cutters are vulnerable to extreme heat and are at risk for heat-related illness and chronic kidney disease, potentially due to high heat strain. We performed a comprehensive assessment of the physiological demands of sugarcane cutters via measurements of metabolic, thermal, and cardiovascular responses. In addition, we assessed cross-shift changes in markers of kidney function. Nine male sugarcane cutters were monitored while working during the spring harvest season in Brazil. Core temperature (Tcore) and heart rate (HR) were continuously recorded, and oxygen consumption was measured during the work shift. Urine and blood samples were collected pre- and postwork shifts. Total sweat loss was calculated using body weight changes and adjusting for water ingestion and urine output. A wet-bulb globe temperature (WBGT) station was used to monitor environmental heat stress. WBGT was ≥30°C on 7 of the 8 study days. Mean and peak Tcore during the work shift were 37.96 ± 0.47°C and 38.60 ± 0.41°C, respectively, with all participants surpassing a Tcore of 38°C. Mean and peak HR during the work shift were 137 ± 14 and 164 ± 11 beats/min, respectively. Percent of maximal oxygen consumption was, on average, 53 ± 11%. Workers had a total sweat loss of 7.63 ± 2.31 L and ingested 6.04 ± 1.95 L of fluid. Kidney function (estimated glomerular filtration rate) was reduced from pre- to postwork shift (Δ -20 ± 18 mL·min·1.73 m2). We demonstrated that sugarcane cutters performing prolonged work during a period of high environmental heat stress display high levels of heat strain, high water turnover, and reduced kidney function.NEW & NOTEWORTHY We demonstrate that a shift of sugarcane cutting performed outdoors during the spring harvest season results in a high level of heat strain. In fact, all the studied workers sustained core temperatures above 38°C and heart rates above 75% of the measured maximum heart rate. Additionally, workers displayed a high water turnover with sweat loss close to 10% of their body weight. Finally, we report elevated muscle damage and reductions in kidney function following the work shift.

A Preliminary Evaluation of the Kidney Function of Sugarcane Cutters From Brazil

OBJECTIVE

To evaluate clinical parameters, markers of kidney function, and skeletal muscle damage in a group of sugarcane cutters during harvesting season.

METHODS

Seventeen volunteers were assessed for anthropometrics and cardiorespiratory fitness. Blood and urine samples were collected 48-hours after the last work session. Blood was analyzed for glucose, creatine kinase, cholesterol, and a complete hemogram. Urine and blood samples were also analyzed for markers related to kidney function.

RESULTS

Volunteers were young (26 ± 6 y), had low body fat (13 ± 5%), and good cardiorespiratory fitness (41 ± 6 mL/kg/min). Classical markers of kidney function (eGFR, creatinine, cystatin C) were within the normal range. However, ten volunteers presented elevated resting serum creatine kinase (221 ± 68 U/L).

CONCLUSION

Manual sugarcane harvesting is associated with sustained skeletal muscle damage which may increase the risk for kidney injury in Brazilian sugarcane cutters.

Heat stress monitoring based on heart rate measurements

Currently, occupational heat exposure is usually measured using environmental variables such as the wet bulb globe temperature index. The costs of heat stress monitoring include the acquisition of specialized equipment and the recruitment of trained personnel. In rapidly changing environments, such as outdoor settings, these assessments must be conducted on a daily basis. The wet bulb globe temperature index has been criticized as a measure of heat stress for its failure to account for individual differences in susceptibility to heat stress, age, body mass index, physical fitness, clothing, illnesses and use of alcohol or drugs. The objective of this study was to assess the relationship between heart rate and body temperature in heat-exposed workers to determine whether heart rate can be used to monitor and prevent heat stress and physiological strain. This study was based on previous literature as well as physiological and environmental data collected from 10 individuals engaged in heavy physical labor. Heart rate, which has been recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) as a possible measure of heat stress, follows a similar trend to body temperature with a slight temporal delay. Heart rate monitors with alarm systems could be developed to notify workers when to slow down their activities or take a break for thermal recovery, thereby contributing to the prevention of heat-related illness.

The heat exposure risk to outdoor workers in Brazil

Heat exposure is a major cause of health issues in outdoor workers. The aim of this study is to show a macro analysis of the heat exposure risk (HER) countrywide through the WBGT index. The index estimates are conducted from 50 years of meteorological observations. The HER takes into account the light, moderate, and heavy workloads, and the HER maps are separately generated decade by decade and season by season. It was found that HER has stronger effect on heavy workload workers during summer. It is even more critical in the Northern, Northeastern, and in part of Midwestern Brazil. There was HER increase in the last two decades, showing the need of applying control measures. It is very important taking continuous actions such as environmental and physiological monitoring, light clothing, and flexible work shifts.

Sobrecarga térmica em áreas rurais: a influência da intensidade do trabalho

Resumo Introdução: a legislação brasileira determina que se monitore o Índice de Bulbo Úmido Termômetro de Globo (IBUTG) nos ambientes de trabalho em que o calor possa representar risco à saúde dos trabalhadores. Porém, esse monitoramento e a adoção de medidas preventivas não são comumente observados. Objetivo: identificar e mapear a influência da intensidade do trabalho na extrapolação potencial de limites de sobrecarga térmica para trabalhadores em atividade a céu aberto em áreas rurais do Nordeste do Brasil. Métodos: com base na Norma Regulamentadora nº 15 e em dados do Instituto Nacional de Meteorologia, o software Sobrecarga Térmica foi utilizado para estimar os índices de IBUTG na região, no período de 1º de setembro de 2016 a 31 de agosto de 2017. Resultados: dos 132 pontos geográficos investigados, a extrapolação dos limites de sobrecarga térmica foi identificada em 48% dos trabalhos pesados e em 14% dos trabalhos moderados, indicando a necessidade de paradas para descanso em mais de 50% do tempo analisado. Discussão: a diminuição da intensidade do trabalho resulta em redução expressiva da sobrecarga térmica. Nas localidades historicamente reconhecidas pelo alto risco de exposição ao calor, deveria ser adotada, como medida efetiva de prevenção, a restrição ao estímulo de atividades extenuantes, sobretudo as promovidas pela remuneração atrelada à produtividade.

[Risk of exposure to heatstroke in sugarcane workers in São Paulo State, Brazil]

Environmental heat is an aggravating factor for sugarcane workers, and manual cane cutting is one of the heavy work activities that favor the generation of metabolic heat. This can combine with other precarious working conditions to produce heatstroke, potentially leading to serious complications and even death. The study aimed to quantify the risk of overheating in sugarcane cutters in São Paulo, Brazil. Drawing on a specific methodology, the study used four years of data to estimate the Globe Thermometer Wet Bulb Index based on light, moderate, and heavy activities. The results showed that the legal limit was exceeded for continuous activity in periods from 1 to 8 hours, which requires control measures in order to continue working. The principal observation was the risk of heatstroke in the three types of activity: light, moderate, and heavy. The limits were exceeded throughout the work shift on 7% of the days for heavy activity and on 3% of the days for moderate activity. In addition, the areas with the highest risk of heatstroke coincide with predominant cane-growing.

Wet-bulb globe temperature index estimation using meteorological data from São Paulo State, Brazil

It is well known that excessive heat exposure causes heat disorders and can lead to death in some situations. Evaluation of heat stress on workers performing indoor and outdoor activities is, nowadays, conducted worldwide by wet-bulb globe temperature (WBGT) index, which calculation parameters are dry-bulb, natural wet-bulb, and globe temperatures, which must be measured at the same time and in location where the worker is conducting his/her activities. However, for some activities performed in large outdoor areas such as those of agricultural ones, it is not feasible to measure directly those temperatures in all work periods and locations where there are workers. Taking this into account, this work aims to introduce a WBGT index estimation using atmospheric variables observed by automatic meteorological stations. In order to support our estimation method, we used, as a test-bed, data recorded in the State of São Paulo (SP), Brazil. By adding the cloudiness factor in the calculation through measurement of solar radiation, the algorithm proved to be as efficient as those mentioned in this work. It was found that this method is viable, with WBGT-estimated values obtained from meteorological data measured by stations with a distance of less than 80 km. This estimate can be used for monitoring heat stress in real time as well as to investigate heat-related disorders and agricultural work.

Análise da contribuição das variáveis meteorológicas no estresse térmico associada à morte de cortadores de cana-de-açúcar

Os cortadores de cana-de-açúcar exercem atividade muito pesada e em condições precárias de trabalho. Além disso, fatores ambientais podem ser um importante agravante à sobrecarga térmica desses trabalhadores. Neste artigo, analisa-se a condição atmosférica no dia da morte de 14 trabalhadores do corte de cana-de-açúcar no Estado de São Paulo, Brasil. Compara-se valores estatísticos históricos da temperatura, umidade, vento e radiação com os valores destas variáveis meteorológicas observadas no dia de cada óbito. Os dados atmosféricos foram obtidos da reanálise do National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). Em 10 dos 14 casos analisados, as temperaturas observadas nos dias dos óbitos foram maiores ou iguais à média somada ao desvio-padrão. Em seis desses casos o valor da temperatura atingiu ou ficou muito próxima do recorde histórico. Constatou-se que a condição atmosférica pode ser um fator importante a ser considerado na análise das condições gerais de trabalho dos cortadores de cana-de-açúcar.