Investigation of chloroxylenol in water environments of Hong Kong and the use of fire extinguisher dry powder to develop latent fingermarks by mass spectrometry

Abstract

Mass spectrometry (MS), a powerful analytical tool, was used to investigate issues in environmental science and forensic science, i.e., investigation of chloroxylenol in water environments of Hong Kong and investigation of the use of fire extinguisher dry powder to develop latent fingermarks. We aimed to understand and address the environmental challenges to protect the natural world, as well as to create new and novel protocols for the collection and analysis of latent fingermarks at crime scenes with the needs of criminal investigations. Chloroxylenol, a halogenated phenolic compound, is an antimicrobial ingredient commonly used in antibacterial hand sanitizers and household disinfectants. Since the Coronavirus Disease-2019 (COVID-19), our habits and lifestyle behaviours have changed, causing a surge in worldwide demand for popular brands (e.g., Dettol, Walch and Ariel) of personal care products (PCPs) in which the main antimicrobial ingredient is chloroxylenol. As a result, enormous amount of chloroxylenol could be released into the aquatic ecosystem through drainage, posing toxicological threat to humans and aquatic animals, such as altered gene expression and histological lesions in freshwater fish. To investigate the extent of chloroxylenol contamination in Hong Kong, water samples were collected from two rivers (Tuen Mun River and Yuen Long Creek) and two sewage treatment plants (Stonecutters Island Sewage Treatment Works and Sha Tin Sewage Treatment Works). Using solid phase extraction (SPE) for sample preparation and ultra-performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-ESI/MS/MS) for identification and quantification, concentrations of chloroxylenol in water samples were determined. Diurnal studies were first conducted, suggesting that the maximum concentrations measured in the river were always correlated with low flow conditions. In Yuen Long Creek, the highest concentration of chloroxylenol was 140 µg/L on January 15, 2022 (Saturday), which may be correlated to the fifth wave of COVID-19 in Hong Kong. For the two sampling campaigns in Yuen Long Creek (January 12 to 22, 2022 and April 13 to 21, 2022), all risk quotient (RQ) values obtained were higher than 1, while the maximum RQ value was over 25, which strongly proved that chloroxylenol is a potential stressor in Yuen Long Creek and possess a high ecological risk to aquatic organisms. Proper river management and regulation are necessary to improve river water quality and protect aquatic organisms. Four typical phenolic compounds (phenol, 2,4-dinitrophenol, 2,4,6-trichlorophenol and pentachlorophenol) were not detected in any of the water samples. At last, the removal efficiencies of chloroxylenol were found to be strongly dependent on the technology implemented in the sewage treatment plants (STPs); biological treatment was found to be highly effective in removing chloroxylenol due to microbial degradation. The results of this study could help health and environmental authorities to plan policies, as well as to raise public awareness of the potential ecological consequences of the use of products containing chloroxylenol. Conventional fingermark detection techniques cannot process large crime scenes and bulky evidence items with large surface areas effectively in a cheap, safe, quick and simple manner. A new and innovative latent fingermark detection technique that uses dry powder from a fire extinguisher was found to detect fingermarks with excellent quality and contrast on nonporous surfaces. The results depicted that fire extinguisher dry powders offered a selective interaction with the moisture and oily components in the fingermark residues, and thus offer clear and sharp images of fingermark ridges, even for latent fingermarks with low deposition quality. Energy dispersive X-ray (EDX) analysis also confirmed the presence of poly(methylhydrosiloxane) (PMHS) with hydrophobic -Si-CH3 groups, as well as the hydrophobic silica micro-particles, which could attribute to the selectivity of fire extinguisher dry powders to fingermark residues. These powders had been proven to outweigh traditional fingerprint powders and cyanoacrylate fuming due to four reasons: (1) cheap and commercially available, (2) safe as particles with average sizes of around 15 µm are large enough to be effectively captured using face masks, (3) high selectivity to fingermarks with weak deposits, such as old fingermarks up to 12 weeks old and (4) quick and simple by spraying the entire crime scene. The results could help forensic scientists to make an informed choice when selecting a detection technique for ‘in situ’ latent fingermarks. To be incorporated into the field of forensic science, the use of fire extinguisher dry powder must be compatible with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) which is a powerful analytical tool to provide both chemical information and spatial information of endogenous and exogenous chemicals in friction ridges. MALDI-MS protocol for fingermark analysis was first optimized and the best results were achieved in the positive mode when using 4 passes of α-cyano-4-hydroxycinnamic acid (CHCA) at a concentration of 5 mg/mL in 70:30ACN/0.1%TFA solution as matrix. The spraying process of fire extinguisher dry powders to develop the latent fingermarks allows the direct analysis of endogenous compounds (e.g., fatty acids, cholesterol esters, diglycerides, wax esters and triglycerides) and exogenous compounds (due to prior handling of a condom, an aspirin pill or personal and household products) embedded in the fingermarks, as well as the imaging of their distributions without disturbing the fingermark patterns. The simultaneous visualization of latent fingermarks and the recording of a chemical profile of the spatial distribution of the chemical species not only provide valuable evidence about the individual such as his/her lifestyle and recent activities, but also resolve overlapping fingermarks which are commonly found at crime scenes. The feasibility of using MALDI-MSI with fire extinguisher dry powders as the new in-situ fingermark development technique was demonstrated. This type of work has never been reported and our results were highly useful to forensic scientists utilizing the full potential of latent fingermarks.