In situ and on-line monitoring of cadmium in soil pore water using an automatic sampling integrated electrochemical sensor

Cadmium (Cd) contamination in soil pore water is the primary pathway for Cd uptake by food crops, such as rice (Oryza sativa L.), posing significant risks to both food safety and human health. This study presents a novel soil pore water metal sensor (SPW-Msensor) for in situ and online monitoring of Cd in soil pore water (Cd_pw). The SPW-Msensor integrates an automated sampling device, comprising a Rhizon sampler and a reciprocating series pump with an independent dual plunger drive, along with a portable electrochemical sensor consisting of a screen-printed electrode, flow cell, and portable potentiostat. The SPW-Msensor enables the detection of Cd within a linear range of 50 to 300 ppb while exhibiting high anti-interference capability. Moreover, it demonstrates excellent repeatability (relative standard deviation values (RSDs) <3.6%) across 30 measurements conducted within a 2-h period. The method exhibits good agreement with results obtained using the standard ICP-MS method (RSDs < 5%). Additionally, this study establishes a positive correlation between Cd_pw detected by the SPW-Msensor and total Cd concentration (Cd_total) in the soil with an R² value equal to 0.89. Data acquired from the SPW-Msensor can be utilized for predicting Cd_total through partial least squares regression modeling, achieving model quality score (Q²) of 0.69, adjusted R² of 0.9345, and root mean square error (RMSE) of 0.1912. The SPW-Msensor demonstrates real-time monitoring capabilities for assessing Cd levels in acidified soils. This SPW-Msensor offers an efficient approach for in-situ and continuous monitoring of Cd_pw that provides valuable insights applicable to environmental and agricultural domains.