# Bioassays with _Allium cepa_ for the Monitoring of Toxicity in the Groundwater of Yucatan, Mexico
## 3 Results and Discussion
### Bioassay  
Nuclear abnormalities were not found in exposed onion roots at any sites or controls. The results of biomarkers are presented in Supplementary Table S4. PCO analysis of the tested biomarkers was able to explain 57.99% of the total variation in the first two axes (Figure 8). CbE, GST, and SOD correlated highly with PCO1. CAT and SOD are highly correlated with PCO2. PERMANOVA indicated no significant differences between sites and controls (\(p\) = 0.7857, Pseudo-F = 0.8373) or between transects (\(p\) = 0.0831, Pseudo-F = 1.76). The _Allium cepa_ test only incorporates the mitotic index, the nuclear abnormalities index, and the growth as toxicity biomarkers. Nevertheless, evaluating other biomarkers, traditionally measured in animal models, is possible since a perfect amount of root biomass is available at the end of the bioassay. Changes in the biomarkers of oxidative stress and inhibition of B-esterases are used to assess exposure and the effects of contaminants in water. The samples presented low concentrations of nutrients, organochlorine pesticides, and PAHs in the present study. Some of these contaminants are reported as cytotoxic and genotoxic. \begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline \multirow{2}{*}{**PAH**} & \multirow{2}{*}{**Month**} & \multicolumn{6}{c}{**Site**} \\ \cline{3-8}  & & **P1** & **P2** & **P3** & **P4** & **P5** & **P6** & **P7** \\ \hline \multirow{2}{*}{Naphtalene} & September & ND & ND & ND & ND & 2.63 & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & 1.59 \\ \hline \multirow{2}{*}{Aeenapthylene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & 2.28 & 3.51 & 2.86 & 7.46 \\ \hline \multirow{2}{*}{Aeenapthrene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Fluorene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Phenanthrene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Anthracene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Fluoranthene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Pyrene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Benzo(a)anthracene} & September & ND & ND & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \multirow{2}{*}{Benzo(b)Fluoranthene + Benzo(k)Fluoranthene & September & 10.93 & 10.63 & 12.07 & ND & 10.48 & 9.40 & 11.56 \\ \cline{2-8}  & October & 14.26 & 9.08 & 12.51 & 9.60 & 9.60 & 7.63 & 8.39 \\ \hline \multirow{2}{*}{Benzo(a)pyrene} & September & ND & 2.88 & ND & ND & ND & ND & ND \\ \cline{2-8}  & October & ND & ND & ND & ND & ND & ND & ND \\ \hline \hline \end{tabular}
\end{table} 
Table 4: PAHs in wells of Yucatan, México in September and October 2021. Values expressed in ng/L. ND: Not detected. Figure 8: Principal Coordinate Analysis (PCO) of biomarkers in _Allium cepa_ roots exposed to well samples in September and October 2021 in wells of Yucatan, Mexico. Triangles are used in samples measured in transect 1 (Sierra Papacal to Chuburná) and circles are used in transect 2 (Nohuayün to Sisal). Colors indicate the site’s proximity to the coast; inland samples are presented from red to green, and the sites nearest to the coast are blue. Figure 7: Principal Coordinate Analysis (PCO) of PAHs and caffeine measured in September and October 2021 in wells of Yucatan, Mexico. Inverted triangles are used in samples measured in transect 1 (Sierra Papacal to Chuburná) and circles are used in transect 2 (Nohuayün to Sisal).