Ultraviolet filters (UVFs) are a diverse group of chemicals found globally in numerous commercial and personal products, especially cosmetics and sunscreens. Their primary role is to protect humans from skin damage resulting from the exposure to ultraviolet rays in the spectrum from UVA (longer λ) to UVB (shorter λ) [1,2]. Formulations can contain several UVFs and other active or inert ingredients in combination, for example to achieve greater mutual photochemical stability or to increase uniformity of application to the skin [3]. It has been reported that 45 organic UVFs are registered for use globally [4], encompassing diverse classes of compounds, the most common being the benzophenones, cinnamates, salicylates, and crylenes [5]. In Canada, the types of UVFs registered for human use by Health Canada include two inorganic chemicals zinc oxide and titanium dioxide, and 19 organic chemicals [6]. In consumer products the maximum concentrations of approved organic UVFs range from <3% (e.g. avobenzone, dioxybenzone) to 15% (homosalate) [6]. Concerns have been raised about biological guidelines in human plasma being exceeded upon typical dermal application of UVFs, such as the accumulation in the placenta of pregnant women [5]. Moreover, UVFs can be metabolized in humans to other stable compounds [7] (e.g. conjugates) or protein adducts [5]. Thus, these compounds have the potential to persist biologically or cause toxicity or endocrine disruption through enterohepatic recirculation.

Organic UVFs are classes of compounds that have been detected in abiotic media such as surface waters [8], [9], [10], marine sediments [11,12], dissolved organic matter [13,14], air [15], as well as in biotic components such as proteins [16], fatty tissues, and liver [4]. The partitioning of organic UVFs to solids and organisms is most likely proportional to their physical-chemical characteristics, especially log KOW [17]. However, it has been demonstrated that experimentally determined solids-water sorption partitioning coefficients (Kd values) are slightly less than estimated based on log KOW possibly due to experimental challenges such as transformation yielding non-target products [10]. Nevertheless, some organic UVFs with greater hydrophobicity fit the criteria for Annex D- information requirements and screening criteria to be included under Annexes A-C as part of the Stockholm convention based on their toxicity, persistence, bioaccumulation, potential for long-range environmental transport, and adverse effects [10]. UVFs are emerging contaminants of concern for several reasons namely oxidative stress [18], genotoxicity [19], estrogenicity [7], and endocrine disruption in both humans and non-target organisms in the environment [20].

Currently, UVFs have no water quality guidelines under the Canadian Council of Ministers of the Environment, nor drinking water quality guidelines under the USEPA [21], EU [22], or WHO [23]. Environmental persistence might occur due to the intrinsic stability of the chemical in question and/or because of constant anthropogenic input (pseudo-persistence) and hence it is important to quantify the UVFs registered for use in Canada in environmental matrices most likely to receive these chemicals (e.g., waste water, recreational lakes, and swimming pools [24], [25], [26]).. The greater levels of chlorine associated with swimming pools might demonstrate added analytical challenges such as altered photostability and the generation of non-target transformation products (TPs) of UVFs [5,13].

It is critical that the parent compounds are stabilized, extracted, and quantified ideally using a single unified method. The suite of UVFs quantified in this method originated from a survey of over-the-counter sunscreens at major local grocers to establish the scope and names of compounds. In addition to previous methods not covering this suite of Canadian approved compounds herein, there are several other drawbacks to these analytical methods. Gas chromatography used in earlier studies is not suitable for all UVFs [10,17,27] as some are hydrophilic and non-volatile necessitating derivatization [4], which this method avoids. Mass analysis via UV-DAD (Diode Array Detector) although quick (and appropriate considering these compounds absorb UV light), suffer the consequences of higher limits of detection than tandem mass spectrometry, and thus not particularly useful in biological (e.g., µmol L−1) [7] and trace environmental concentrations (i.e., ng L−1 to µg L−1) [11,17]. Moreover, some UVFs simply do not ionize efficiently in either a single positive or negative mode method using electrospray ionization (ESI) necessitating separate runs and calibration curves unless protocols for polarity switching can be established.

These analytical novelties notwithstanding, there are previous studies of UVF extraction from aqueous matrices using solid phase extraction [17]. These include C18 hydrophobic and proprietary variations of the hydrophilic-lipophilic balance sorbents (e.g. StrataX®, Oasis HLB®) [17]. As the suite of UVFs in this study range in hydrophobicity (log KOW- Table 1) from 0.88 (sulisobenzone) to 7.35 (octocrylene) HLB was chosen for extraction purposes. HLB is essentially a macro-porous copolymer poly(divinylbenzene-co-N-vinylpyrrolidone) and is suitable for a range of physical-chemical properties [28]. However, given the variation of accuracies for UVFs in previous LC-MS/MS studies using 1 or 2 internal standards [11,12,29,30], it is important to include as many of the matching isotopically-labeled standards as possible for more robust quantitation of UVF recovery and precision. Moreover, the eight UVFs herein have not been previously extracted concomitantly, which are the major novelties of this study.

This study sought to develop a single solid phase extraction method coupled to a single mass analysis method using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and polarity switching for the determination of eight of the most popular and frequently used UVFs in Canada. The UVFs are avobenzone, dioxybenzone (benzophenone-8), homosalate (3,3,5-trimethylcyclohexyl salicylate), octinoxate (2-ethylhexyl-trans-4-methoxycinnamate; EHMC), octisalate (ethylhexyl salicylate; EHS), octocrylene, oxybenzone (benzophenone-3), and sulisobenzone (benzophenone-4).