Identification and Characterization of Mercury Contamination in Vegetables and Herbs Cultivated on a Commercial Vertical Indoor Farming System with Light-Emitting Diode Lighting: Unveiling an Unusual Food Safety Risk of Some Improperly Manufactured High-Density Agricultural Production Systems

Abstract

Artificial grow lights, such as light-emitting diodes (LEDs) and fluorescent grow lights, are commonly used in modern day indoor farming, citing advantages in energy efficiency and a higher controlled environment. However, the use of LEDs poses a risk in mercury contaminations as a result of its production process, specifically LEDs with polyurethane encapsulates that were traditionally produced using mercury resins as a catalyst. A total of 10.0 ppm of mercury was detected in a curly kale sample harvested from an indoor hydroponic vegetable farm, exceeding Singapore Food Regulation's limit of 0.05 ppm. Vegetables, farming inputs, and surface swabs from the affected farm were analyzed using wet acid digestion followed by cold vapor atomic absorption spectroscopy analysis. The investigation found high concentrations of mercury in the LED encapsulant, and the encapsulant material was identified to be polyurethane by Fourier transform infrared spectroscopy and pyrolysis−gas chromatography−mass spectrometry analysis, indicating the source of mercury contamination to be the LED polyurethane encapsulant.

Addressing the safety of new food sources and production systems

“…The lights and installations used in vertical farms can raise food safety concerns as certain materials can introduce hazardous chemicals into the plant growth media or deposit these chemicals onto plant surfaces. For example, mercury vapor released from urethane-based materials used in light emitting diode lamps has been found to deposit on plants (Ng et al, 2023). This highlights the importance of having a comprehensive awareness of safety aspects of inputs and infrastructure used in vertical farms.…”

“…The importance of multi-stakeholder discussions to advance food safety aspects of NFPS is discussed further in Section 4.5. (Ng et al, 2023) Potential deposition of hazardous materials, such as asbestos and microplastics (Buscaroli et al, 2021) 3D food printing Potential biofilm-forming pathogenic bacteria, such as E. coli, S. aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa (Hall et al, 2021;Jackson et al, 2023) Potential microbial contamination if food processing side streams are used (Wang et al, 2019) Potential hazards if food processing side streams are used (e.g., solanine from potato peels) (Maga & Fitzpatrick et al, 1980) Potential migration of chemicals from food contact materials (Formlabs, 2019) Potential migration of small particles from food contact materials (Formlabs, 2019) Potential food products that may be too sharp or hard (Zhang et al, 2022) Abbreviations: LED, light emitting diode; POPs, persistent organic pollutants.…”