Electrolyte Imbalance and Indirect Indicators of Dehydration in Temporary Agricultural Workers Exposed to Extreme Heat in the Mediterranean: An Observational Study on Environmental Health Risks

<b>Background:</b> Climate change is intensifying extreme heat exposure in Mediterranean agricultural systems. Migrant workers engaged in outdoor fieldwork are a highly vulnerable population with limited access to resources. Crucially, there is a notable lack of data on how heat affects these workers in this specific region. <b>Objective:</b> This study aimed to analyze the physiological effects of high-temperature exposure by quantifying and correlating indirect indicators of dehydration and electrolyte imbalance (sodium and potassium losses, sweat, body weight, and blood pressure). <b>Methods:</b> An observational study was conducted over nine consecutive days involving ten agricultural participants, yielding 90 observations. Measurements of body weight, heart rate, blood pressure, skin temperature, sweat loss, and sodium and potassium concentrations were taken before, during, and after daily field activity. <b>Results:</b> Results showed considerable interindividual variability in thermophysiological responses. Participants lost an average of 0.8 kg (range -9.1 to +3.6 kg) and produced 3.91 L of sweat (range 1.9-6.4 L), with sodium and potassium losses of 4932 mg and 646 mg, respectively. Sweat loss correlated with sodium (r = 0.414, <i>p</i> = 0.001) and potassium (r = 0.791, <i>p</i> < 0.001), and diastolic blood pressure was moderately associated with weight loss (r = 0.576, <i>p</i> = 0.016). <b>Conclusions:</b> Sweat loss was the main driver of electrolyte depletion, with marked interindividual variability. Monitoring sweat-related indicators and diastolic blood pressure could help detect dehydration risk in agricultural workers exposed to extreme heat. Targeted hydration strategies and occupational health education are essential to mitigate these risks.