Bioaccumulation of Perfluoroalkyl Substances in African marigold (Tagetes erecta L.) used for Diabetes mellitus Management and in Diabetic Serum of a South African Population

Abstract

Polyfluoroalkyl substances (PFASs), including perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are anthropogenic chemicals. For more than half a century, these long-chain compounds have been used in a wide range of industrial applications, such as the manufacturing of consumer products, ranging from grease-proof food packing to aqueous fire-fighting foams and to stain repellents such as Teflon®. Subsequently, these ubiquitous contaminants which are environmentally persistent, toxic, and bioaccumulative, have been a focus of public concern worldwide. Hence, due to public health apprehensions and environmental risks posed by PFASs, their manufacturers and various environmental agencies decided on restricting their use, and whereby the use of these chemicals could not be stopped, their replacement by other alternative chemicals was suggested. Therefore, per- or polyfluorinated carbon chains, e.g. perfluorobutane sulfonate (PFBS), which has been regarded as one of the most important short-chain PFASs and less harmful to the environment at large. However, a systematic review from the current work reveals that physicochemical properties of short-chain PFASs are not different from their predecessors thus suggesting that short-chain PFASs are as harmful as their homologues. Similarly, the literature reviewed demonstrated how novel technologies have also been proven to be incapable of removing these substances, including to short-chain PFASs, from various environmental matrices. Moreover, plant species have extensively been susceptible to PFASs, and various other POPs accumulation. However, the mechanisms that led to their uptake and storage by plants stayed unknown until proteins belonging to the family of major intrinsic proteins (MIPs) and ater named as Aquaporins (AQPs) were discovered. Hence, the present work has reported that there are diverse AQPs in plants than in mammals, with specific functions, even though first reports on these proteins suggested that their significant impact was water for transportation only. To date, it is well known that plant AQPs possess subclasses or isoforms. Some of these include SoPIP2;1 and AtTIP2;1, prevalent in Spinacia oleracea and Arabidopsis thaliana, respectively. We report that these two isoforms have individual pore diameters or sizes: SoPIP2;1 (2.1 Å) and AtTIP2;1 (3 Å), which might play a role in the selectivity process of molecules which pass through the water transportation channels of the concerned plants. This ultimately suggested SoPIP2;1 pore diameter serving as a pathway of smaller molecules, while AtTIP2;1 pore diameter would serve as a conduit for both smaller and larger compounds. As such, the pore diameters of these two isoforms made them potential conduits of PFASs whose carbon–fluorine bond typical size is 1.35 Å, much smaller than that of AtTIP2;1_2.1 Å and PIP2s, i.e. SoPIP2;1_3 Å, thus substantiating the uptake and ultimate storage of PFASs by plant species. Subsequently, the uptake and storage of PFASs and other POPs by plants have been proven to lead to unprecedented environmental and human risks. As plants with the potential to heal or manage certain ailments, such as Diabetes mellitus (DM), when exposed to PFASs, it was necessary to substantiate such a phenomenon. This current study further determined the propensity of PFASs, such as PFOA, PFOS and PFBS, to accumulate in a plant commonly used in the management of DM, namely the African marigold (Tagetes erecta L.). The study was important as this plant is used in diabetes management in the Western Cape, South Africa, thus implying the plant being a pathway through which humans might be exposed to PFASs and its precursors. Accordingly, the target analytes of the study, PFOA, PFOS and PFBS, were identified and quantified in samples collected from the said plant, i.e. Tagetes erecta L., in contaminated river water used to irrigate the studied plant, as well as diabetic serum samples from patients likely to use the plant. The analysis was done using a liquid chromatography coupled with tandem mass spectrometry (Shimadzu LCMS-8030, Canby, OR, USA). The MS operational conditions were sourced with an MS interface electrospray ionisation in negative ion mode. A multiple reaction monitoring (MRM) mode of analysis was used to quantify the targeted PFASs in samples. Hence MRM transition for PFOA, PFOS and PFBS being of 413.00 > 368.95 (acquisition time: 8.6 min), 499.00 <80.15 (8.9 min) and 299.00 > 80.10 (6.8 min), respectively. A Luna® Omega Polar C18 column (2.1 × 100 mm, 3.0 µm, Phenomenex, Aschaffenburg, Germany), with 40 °C in temperature, assisted in the separation of the analytes. The mobile phase at a flow rate of 0.3 L/min was made of 20 mM ammonium acetate and MeOH (100%). The process followed (for solid samples, i.e. plants) (n = 8) was: 1) sample drying, 2) milling, 3) screening, 4) digestion, 5) sonication, 6) filtration, 7) Solid phase extraction (SPE), 8) analyte elution and 9) analysis; for water samples (n = 20) the process was: 1) filtration, 2) SPE, 3) analyte elution and 4) analysis; while for serum samples (n = 179) the process was: 1) sample uptake, 2) buffers, 3) Mix, 4) centrifuge, 5) Dissolve, 6) filtration, 7) SPE, 8) conditioning, 9) elution, 10) reconstitute, 11) analysis. PFOA, PFOS and PFBS were observed in all the plant samples and were found in concentrations of up to 94.83 ng/g, 5.03 ng/g, and 1.44 ng/g, for PFOA, PFOS and PFBS, respectively. Similarly, PFOA, PFOS and PFBS were identified in all the river water samples and were found in concentrations ranging between 1.15 to 107.82, 1.24 to 20.75 and ND to 0.06 ng/L for PFOA, PFBS and PFOS, respectively, for regime A (winter/wet season) and <LOQ to 4.35, 1.89 to 5.29, and <LOQ to 0.06 ng/L for PFOA, PFBS and PFOS, respectively, for regime B (summer/dry season). As the river water analysed in the current study showed concentration levels of PFOA, PFOS and PFBS in comparison to the studied plant (i.e.Tagetes erecta L.), the prevalence of these substances in river water samples which was used to irrigate the studied plant suggests that contaminated water sourced for plant irrigation purposes such as in impoverished communities in South Africa, will ultimately result in the irrigated plant’s contamination. Hence, the bioconcentration factor (BCF) in the present study has indicated the African marigold’s affinity to PFAS accumulation. The BCF for PFOA, PFOS and PFBS was in the range 0.48 to 2.52, 4.00 to 167.67 and 0.05 to 0.31, respectively. Thus, the studied plant, i.e. Tagetes erecta L., demonstrated a high bioaccumulation potential for PFOS. Furthermore, PFOA, PFOS and PFBS were detected in all the serum samples (n = 179) of individuals suffering from DM, who are likely to use Tagetes erecta L. in order to determine whether there is a direct correlation between PFOA, PFOS, PFBS with known cases of DM. The patients are from a Bellville South population, in Cape Town, South Africa, who are of mixed-ancestry origin with the second highest prevalence of diabetes in South Africa. PFOA, PFOS and PFBS concentrations of up to 4.74, 0.77 and 1.27 ng/L were detected in males, respectively; and 10.73, 1.06 and 1.77 ng/L in females, respectively; with PFBS being the second most abundant PFAS in the sera, after PFOA; albeit, no significant association was found between the investigated PFASs and DM, but a significant correlation trend was detected between PFOA and individual anthropometric and biochemical measurements.