Pollen grain abortion as indicator of mercury pollution near gold mining sites in Camarines Norte [Philippines]

Based on the results of the study, the metal mercury caused pollen grain abortion of the studied plants both in the field and in laboratory experimentation. Statistical analyses of pollen grain abortion by ANOVA using the SAS system showed that there was a significant difference between the controls and contaminated materials at 0.05 level of significance. The p-value computed for the three species (Cleome ratidosperma, Ludwigia micrantha and Stachytarpheta jamaicensis) obtained from the field during the rainy season, all the species studied gave a p-value of 0.0001. For plants grown in the laboratory, the p-value obtained was 0.0001 for all the species. Pollen abnormalities exhibited by the four species indicating aborted condition included a) staining deficiency, and b) reduced pollen sizes. Two types of staining deficiencies were observed: 1) absence of protoplasm due to the pollen's inability to absorb stain, and 2) incomplete development of protoplasm because only a part of it is distinct. Of the four species studied, S. jamaicensis and C. diffusa are found to be the best bioindicators of mercury pollution. C. rutidosperma may be used, however, when determining only the presence of contamination. L. micrantha, on the other hand, is not a good bioindicator for this purpose because its sensitivity to other factors in the environment, aside from mercury, make it unreliable for monitoring this type of pollution. These factors are probably heat stress and water deficit as shown by the results on higher pollen abortiveness obtained from the field, in spite of lower mercury content in the plants' tissues, and this observation has not been shown by plants grown under controlled conditions. Although C. diffusa and S. jamaicensis also exhibited the same behavior, there was higher variability in L. micrantha than those of the two former species. In terms of bioremediation ability, all the four species studied may be used to clean up mercury contaminated environments with C. rutidosperm highly recommended for locally occurring plants due to its sturdy nature and its ability to survive even in unfavorable conditions. C, diffusa and S. jamaicensis, on the other hand, are preferred when using introduce plants because of their ability to preferentially accumulate mercury in their roots