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ChemometriC a n d a n a l y t iC a l strategies f o r t h e s t u d y o f s o i l s f r o m m a r i t i m e an t a rC t iC a use of an autosampler that spends at least 10 s for each sample. The STAT-FAAS became an interesting strategy for fast sequential determination of Cd and Pb, because it combines high analytical throughput (the same observed by FS-FAAS) and good LODs (limits of detection, defined by IUPAC as three times the standard deviation of the blank (n=10) divided by the slope of the calibration curve) with intermediate values between the conventional FAAS and TS-FF-AAS. The poorer performance of TS-FF-AAS in the fast-sequential mode, in relation to analytical throughput, for Cd and Pb determination, is due to the signal stabilization time (60 s for each sample) before starting the measurements. 3.4. chemometrIc treatment o f s o Il c h e m Ic a l a n a l y s e s: metal c o n c e n t r a t Io n s a n d s o Il c h a r a c t e r I s t I c s For the HCA, the data were organized in a matrix with 28 rows (number of samples) and 29 columns (investigated variables, expressed as the average of three replicates). The variables investigated were the pseudototal concentrations of Cd, Cr, Cu, Mn, Ni, Pb and Zn; the bioavailable concentrations of Cd and Pb; the percentage at each step of the SEP and the sum of the three initial fractions related to the labile portion of Cu, Mn and Zn; and finally, soil characteristics (pH, TOC and granulometry, including the percentages of sand, silt and clay), totaling 29 variables. The data were autoscaled and, for dendrogram calculation, the Euclidean distance and incremental linkage methods were used. The HCA results are shown in Fig. 3. The dendrogram exposed remarkable differences between soil samples around the station (especially those impacted by the oil tanks) and the samples further from Ferraz, as seen by the formation of two groups of samples at each sampling region. The control points around Ferraz Station, points 1 and 6 (see fig. 1), had chemical characteristics similar to those points further from Ferraz, as seen from their position in the dendrogram (Fig. 3). These results confirm the preliminary analysis performed with the combination of SR-XRF and PCA, which identified differences between the samples of the 2 sites. For PCA application, some of the variables were discarded to facilitate the analysis interpretation. In the same fashion as for HCA, fractions 1, 2 and 3 of SEP for each element (Cu, Mn and Zn) were combined. All data were then organized in a matrix with 28 rows (number of samples) and 17 columns (related to the variables). This matrix was autoscaled to give the same importance to all variables, and the PCA was applied. The scores and loadings of the PCA plot are shown in Fig. 4a and 4b. A large separation was observed between the sampling sites (Fig. 4a, scores plot) and the variables related to this behavior, as seen in Fig. 4b. Points directly impacted by the oil tanks had the highest concentrations of Cr, Ni and Pb. Table III confirms that the points directly affected by Ferraz oil tanks had higher concentrations of Cr, Ni and fi g u rE 3. hCa (d E n d ro g ra m) w i t h all d a t a o B t a i nE d f ro m thE quantitativE d E t E r m i n a t i o n o f m E t a l s a n d s o i l CharaCtEristiCs. 154 Br J Anal Chem
Pl a C E / ma t r i x rEfErEnCE Pb. Lead was enriched by about 5-fold at points around the diesel tanks, compared to points further from the station. However, the highest concentrations for Pb were still below the guideline value for soil quality and slightly higher than the prevention value, according to CETESB [49], the environmental agency of São Paulo State, Brazil. The Cr concentrations at the most impacted sites reached more than 300 mg kg -1 , higher than the guideline value for soil quality. Finally, Ni was slightly enriched in the most affected samples, exceeding the www.brjac.com.br taBlE iii. ComParativE taBlE w i t h C o n C E n t ra t i o n s o f Cr, ni a n d PB in s o i l samPlEs o f sElECtEd PaPErs. Cr (m g/kg) ni (m g/kg) PB (m g/kg) ra n g E av E r a g E ra n g E av E r a g E ra n g E av E r a g E nE a r fE r ra z o i l t a n k s 1 This study 31.2 – 300.1 190.3 2.6 – 36.1 12.3 7.6 – 105 38.2 fa r f ro m t h E station 1 This study 15.4 – 272.3 68.3 4.2 – 16.8 8.5 5.65 – 9.05 7.45 fE r ra z station s o i l s 2 sh a n g h a i u r B a n s o i l s 3 vi E t n a m r u ra l s o i l s 4 vi E t n a m u r B a n s o i l s 4 ma ra m B i o station 5 mC m u r d o station (g ra y s o i l) 6 mC m u r d o station (rE d s o i l) 6 Santos et al.. [10] Shi et al.. [50] Thuy et al.. [51] Thuy et al.. [51] Chaparro et al.. [9] Crockett [8] Crockett [8] Unavailable 40 Unavailable 5.1 Unavailable 11.5 25.5 – 233.3 107.9 4.95 – 65.7 31.14 13.7 – 192 70.7 80.8 – 116.7 98.5 11.0 – 31.5 21.6 0.8 – 3.2 1.9 23.2 – 174.5 92.2 9.4 – 67.9 22.6 0.4 – 20.1 3.6 Unavailable 22 Unavailable 5.1 Unavailable 10.2 95 – 249 172 77 – 119 98 1.0 – 10.6 5.8 154 – 480 317 137 – 215 176 3.7 – 6.3 5.0 guidElinE v a l u E 7 DEFRA [52] 200 75 450 PrE v E n t i o n v a l u E 8 CETESB [49] fi g u rE 4. PCa graPhs o f sElECtEd d a t a in a sCorEs P l o t (a) a n d l o a d i n g s P l o t (B). 75 30 72 Guerra et al. value prescribed by CETESB [49]. Table III also shows a comparison between concentrations of Cr, Ni and Pb in this work and some selected soil samples around the world. Inherent characteristics of soil samples such as granulometry, pH and TOC are important variables related to the observed discrimination between the sampling sites. In the samples collected around Ferraz, granulometry and TOC, in particular, are closely related to the highest bioavailable concentrations of Pb and to 155
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