Seventeen (60.7%) samples presented mercury content below the LOD, and seven samples (25%), below the
LOQ. The mercury contents of only four samples were above the LOQ but below the maximum limit established by international guidelines, increasing from 11.62 to 14.48 [micro]g/kg in samples FO23, FO15, FO4, and FO9.
In the latter, more than 80% of the samples evidenced values < LOD and no sample had values higher than the
LOQ. Although the areas of activity (grouped cooperatives) did not show significant differences in the frequency of values in the three categories (<LOD, between LOD and LOQ, and >LOQ), the observed Hg concentrations suggest increased exposure in the pile, scale and conveyor belt when compared to other activities.
The lowest concentrations assayed where the signal/noise ratio was at least 10:1 was regarded as the
LOQ. The LOD was defined as a signal/noise ratio of 3:1.
(b) Congeners with values higher than
LOQ. ND=Not detected.
Sensitivity of the method was evaluated by determining LOD and
LOQ. They were determined based on the standard deviation of the response and the slope of the calibration curve.
Limit of detection and limit of quantification were determined by injecting the standard solution until the signal to noise ratio (S/N), was about 3 for LOD and 10 for
LOQ. The LOD and LOQ were experimentally verified by ten injections of lycorine.
The intercept at zero concentration (S[D.sub.0]) obtained by extrapolation of the curve was used to evaluate the LOD and
LOQ. The LOD was calculated as the 3 * S[D.sub.0] and LOQ was 10 * S[D.sub.0] [19].
LOD and
LOQ. Limit of detection (LOD) was calculated based on the standard deviation of the response and the slope.
The limits were empirically determined using concentrations that produced signal-to-noise ratios of 3 for LOD and 10 for
LOQ. Values determined for analysis using UPLC-MS/MS are reported as picomoles/gram blood as follows: [C.sub.6]/[C.sub.8]PFPiA, LOD: 0.0050, LOQ: 0.025; [C.sub.8]/[C.sub.8]PFPiA, LOD: 0.0020, LOQ: 0.022; [C.sub.6]PFPA, LOD: 0.050, LOQ: 0.10; [C.sub.8] PFPA, LOD: 0.080, LOQ: 0.40; perfluorohexanoic acid PFHxA, LOD: 0.64, LOQ: 1.3; perfluoroheptanoic acid (PFHpA), LOD: 0.55, LOQ: 1.1; perfluorooctanoic acid (PFOA), LOD: 0.77, LOQ: 0.97; perfluorononanoic acid (PFNA), LOD: 0.43, LOQ: 0.86.
The concentrations of hazardous substances in the rivers in most cases did not exceed the established environmental quality standards and were prevailingly below the
LOQ. Only the contents of a few phthalates, e.g.
The concentrations of lead and molybdenum were all below the
LOQ. For all other elements investigated there was a greater tendency to accumulate in the visceral tissue.