Identification of Pelargonium radula as bioindicator for mercury (Hg) detection confers a new hope for monitoring the safety of drinking water consumption. Hg, like other non-essential metals, inflicts the deterioration of biological functions in human and other creatures. In the present study, effects of Hg on the physiology and biochemical content of P. radula were undertaken to understand the occurrence of the morphological changes observed. Young leaves of P. radula were treated with different concentrations of Hg-containing solution (0.5, 1.0 and 2.0 ppb) along with controls for 4 h, prior to further analysis. Elevated Hg concentration in treatment solution significantly prompted an increased accumulation of Hg in the leaf tissues. Meanwhile, total protein, chlorophyll and low molecular mass thiol contents (cysteine, glutathione and oxidized glutathione) decreased as Hg accumulation increased. However, phytochelatin 2 productions were induced in the treated leaves, in comparison to the control. Based on these findings, it is postulated that as low as 0.5 ppb of Hg interferes with the metabolic processes of plant cells, which was reflected from the morphological changes exhibited on P. radula leaves-the colour of the Hg-treated leaves changed from green to yellowish-brown, became chlorosis and wilted. Changes in the tested characteristics of plant are closely related to the Hg-induced morphological changes on P. radula leaves, a potential bioindicator for detecting Hg in drinking water.

Pollution by organic and inorganic toxic substances has raised public and environmental concern globally since last decade. However, due to rapid growth of world population along with excessive industrial development, this situation worsens. One of the non-essential heavy metals, mercury (Hg), is a widespread toxic pollutant commonly found in drinking water sources. Therefore, there is a need to monitor the level of Hg in the drinking water. Biomonitoring, which use biological response to assess environmental changes, is one of the approaches that are getting more attention recently. Plant bioindicator offers huge advantages over conventional water quality analysis. Other than cheap, easy to apply and give rapid results; most importantly, people in the rural area can apply this method to monitor water quality without the need of modern equipment and technical expertise. In this study, young leaves from terrestrial plants were treated with water containing Hg solutions. Plant that showed visible morphological changes was selected as potential bioindicator and further analyzed. Over 60 plants were screened including herbs, shrubs and flowering plants. At the 24th h of observation, 15 plants showed morphological changes with several obvious symptoms, including the presence of dark spot, chlorosis, browning of leaves and wrinkle. Among these plants, Plectranthus amboinicus, Lantana camara and Pelargonium radula treated with Hg solutions exhibited morphological changes at the 6th h of treatment, compared to the control. In the present study, Pelargonium radula was chosen as the Hg bioindicator as it gave the fastest and visible morphological changes, which is within 4 h of treatment. This new finding was promising, as it demonstrated that plants could be used for Hg biomonitoring for the safety of drinking water.