Data on quantification of PAHs and elemental content in dry Camellia sinensis and herbal tea

Here we present data on potentially toxic metals and polycyclic aromatic hydrocarbons (PAHs) in commercially sold tea brands in Nigeria. The article provides data on the sequential extraction and the pseudo-total concentrations of eight metals (Cd, Cr, Cu, Mn, Ni, Pb, V and Zn) and polycyclic aromatic hydrocarbons (PAHs) in dry Camellia sinensis and herbal tea. The three-step Community Bureau of Reference (BCR) method and acid digestion with aqua regia were adopted for sequential and total metal extractions, respectively. The extraction of branded tea samples for PAHs analysis has been described in “Concentrations, sources and risk characterisation of polycyclic aromatic hydrocarbons (PAHs) in green, herbal and black tea products in Nigeria” [1] and “Polycyclic Aromatic Hydrocarbons (PAHs) Occurrence and Toxicity in C. sinensis and Herbal Tea” [2]. Elemental and PAHs analyses of extracts were determined by Microwave Plasma Atomic Emission Spectroscopy (Agilent MP-AES 4100) and Agilent gas chromatograph 7890A coupled with flame ionization detector (FID), respectively.


Experimental factors
Tea samples were oven-dried, milled, and later extracted using the Community Bureau of Reference (BCR) method. Samples for pseudototal analysis for were digested using a mixture of conc. HCl (37%, Sigma Aldrich) and HNO 3 (70%, BDH) in the ratio 3:1. For PAHs, 0.5 g of each tea sample was extracted using N-hexane.

Experimental features
Elemental content determined using MP-AES. PAHs analysis using GC-FID. Data source location Lagos and Ogun state, Nigeria. Data accessibility Data included in this article. Related research article "Chemical speciation and characterization of trace metals in dry Camellia sinensis and herbal tea marketed in Nigeria" (Fred-Ahmadu et al., 2018, In press) [3]. "Levels of polycyclic aromatic hydrocarbons (PAH4) in some popular tea brands in Nigeria."   [4].

Value of the data
The data provides information on the elemental concentrations of green, herbal and black tea brands commonly consumed in Nigeria.
The quantification data on US-EPA priority PAHs is provided in some selected tea samples. The data could be used in assessing the degree of risks associated with heavy metals and PAHs exposure.
The acquired fractionation data will be advantageous for the scientific community interested in assessing the mobility and bioavailability of metal species.

Data
This data article presents fractionation, pseudo-total elemental and PAHs concentrations twentythree dry tea samples. Table 1 presents the brand names of the tea products and their sample codes adopted for this study. The BCR sequential extraction procedure is showed in Table 2. The mean concentrations of heavy metals in the various fractions (F1, F2, F3 and F4) are represented in Tables 3-5, respectively. Table 6 shows the mean pseudo-total concentrations. The total PAH concentrations in Camellia sinensis, herbal and black tea samples are shown in Figs. 1-3.

Sample collection and preparation
Twenty-three (23) tea samples (including 11 green, 8 herbal and 4 black tea brands) were purchased from supermarkets in Lagos and Ogun states, Nigeria. The manufacturers' information for each brand of tea was recorded. Samples were weighed and oven-dried at 105°C for 30 min. Sample size was reduced and homogenized by coning and quartering, followed by milling in a clean porcelain mortar before sequential and pseudo-total extraction procedure ( Table 2). Samples meant for PAHs analyses were not subjected to oven drying procedure.

Sequential extraction
See Table 2. LGB USA Lipton Green Tea (lemon and ginseng) LGL USA Lipton Green Tea (red goji raspberry) LGR USA Lipton Green Tea (jasmine passion with fruit) LGJ USA

Acid digestion for pseudo-total elemental contents
Aqua regia was prepared in a 3:1 ratio of concentrated HCl and HNO 3 . Then 1.0 g of the dry ground tea sample was weighed into a 250 mL conical flask. Fifty (50) mL of aqua regia was added to the sample and the conical flask was transferred to a Stuart heat-stir hot plate to heat at controlled temperatures between 50°C and 250°C for about 2 hours in the fume cupboard. Additional twenty (20) mL of aqua regia was added as the volume reduced until a clear solution was obtained. The cold solution was filtered and made up to 100 mL with deionized water in a 100 mL volumetric flask and taken to the MP-AES for analysis.

Calibration curves
The standard stock solution (1000 mg/L BDH grade) was appropriately diluted to prepare the calibration standards of each heavy metal determined. Stock solutions of 0.5, 1.0 and 2.0 mg/L of Cd, Cr, Cu, Mn, Ni, Pb, V and Zn were used to establish the calibration curves. The limit of detection (LOD) and limit of quantitation (LOQ) were determined using data from the calibration curves as 3 and 10 times the standard deviation of the standards, respectively (Table 7). Recovery study was carried out for an assessment of the analytical measurement procedure.