Feasibility of Radio Frequency Based Wireless Sensing of Lead Contamination in Soil

Feasibility of Radio Frequency Based Wireless Sensing of Lead Contamination in Soil Yixuan Gao yixuan@cs.cornell.edu Cornell Tech New York, USA Tanvir Ahmed tanvir@infosci.cornell.edu Cornell Tech New York, USA Mikhail Mohammed mikhail.mohammed05@bcmail.cuny.edu Brooklyn College of the City University of New York New York, USA Zhongqi Cheng ZCheng@brooklyn.cuny.edu Brooklyn College of the City University of New York New York, USA Rajalakshmi Nandakumar rajalakshmi.nandakumar@cornell.edu Cornell Tech New York, USA ABSTRACT Widespread Pb (lead) contamination of urban soil significantly im- pacts food safety and public health and hinders city greening efforts. However, most existing technologies for measuring Pb are labor- intensive and costly. In this study, we propose SoilScanner, a radio frequency-based wireless system that can detect Pb in soils. This is based on our discovery that the propagation of different frequency band radio signals is affected differently by different salts such as NaCl and Pb(NO3)2 in the soil. In a controlled experiment, manu- ally adding NaCl and Pb(NO3)2 in clean soil, we demonstrated that different salts reflected signals at different frequencies in distinct patterns. In addition, we confirmed the finding using uncontrolled field samples with a machine learning model. Our experiment re- sults show that SoilScanner can classify soil samples into low-Pb and high-Pb categories (threshold at 200 ppm) with an accuracy of 72%, with no sample with > 500 ppm of Pb being misclassified. The results of this study show that it is feasible to build portable and affordable Pb detection and screening devices based on wireless technology. CCS CONCEPTS • Computer systems organization →Sensor networks; • Hard- ware →Sensor applications and deployments; • Computing methodologies →Machine learning approaches. KEYWORDS Sensing Application, Urban Health, Soil Lead Contamination, Signal Processing, Machine Learning 1 INTRODUCTION Urban soils are significant resources and provide essential ecologi- cal services such as growing produce, assimilation of organic waste, stormwater management, greening cities, improving air and water quality, and combating urban heat island effects [4]. However, nu- merous studies have shown that urban soils are often contaminated, primarily due to historical and current anthropogenic activities [28]. Lead (Pb), an invisible, odorless neurotoxin, is of particular con- cern, given its widespread presence in the environment and strong association with neurocognitive disorders and aggression in adoles- cents - especially for children [1, 24]. Pb is found to be present at elevated levels in urban soils worldwide. In New York City, it was found that over 50% of the garden soils tested contained more than 400 parts per million (ppm) of Pb – the previous general threshold set by the U.S. Environmental Protection Agency (EPA) and the New York State Department of Environmental Conservation [5]. In an official statement released on January 17, 2024, to strengthen the safeguards to protect families and children from Pb-contaminated soil, the U.S. EPA lowered the screening level for Pb in soil at resi- dential properties from 400ppm to 200ppm [10], which is now the current screening standard. There is an urgent need to screen ur- ban soils for traces of metal contaminants (such as Pb) as they can significantly impact public health and the safety of food grown in urban community gardens [22, 25]. Currently, composite soil samples are commonly sent to commer- cial or academic laboratories for analysis, utilizing chemical process- ing techniques and advanced instrumentation. Such analysis tends to require substantial labor and incur significant expenses [34], and thus poses challenges for many urban communities. These commu- nities, often characterized by economic disadvantages, a prevalence of minority or marginalized populations, and a disproportionate burden of environmental contamination, face particular difficulties in accessing related resources. Furthermore, soil Pb is highly het- erogeneous at a small scale, even within the same garden [12, 15]. Pb levels can vary by more than an order of magnitude at different locations within the same garden [3]. Thus, a composite soil sample is not able to reveal such variations and will miss hotspots that may pose the most health risks. While Portable X-Ray Fluorescence (pXRF[40]) has emerged as a handy tool for in-situ (or lab) screening of Pb and other metals in soils [11, 19, 27, 30, 33, 35, 42], the in- strument typically costs $20,000-60,000, which is not affordable for most communities. Therefore, there is a need to develop low-cost alternatives to detect Pb in situ, so as to be able to accurately map sites for contamination. This study aims to address this need by examining the feasibility of developing an accessible and affordable Radio Frequency (RF) based wireless sensor that can monitor Pb. As a rapidly emerging technology, radio f

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