Giant Duckweed (Spirodela polyrhiza) Root Growth as a Simple and Sensitive Indicator of Copper and Chromium Contamination

Aquatic environment are often contaminated with heavy metals from various industrial sources. However, physicochemical techniques for pollutant detection are limited, thus prompting the need for additional bioassays. We investigated the use of greater duckweed (Spirodela polyrhiza) as a bioindicator of metal pollution. We exposed S. polyrhiza to four pollutants (namely, silver, cadmium, copper, and chromium) and assessed metal toxicity by measuring its frond area and the length of its regrown roots. The plant displayed significant differences in both frond size and root growth in response to the four metals. Silver was the most toxic (EC50 = 23 mu g L-1) while copper the least (EC50 = 365-607 mu g L-1). Direct comparisons of metal sensitivity and the reliability of the two endpoint assays showed that root growth was more sensitive (lower in terms of 50% effective concentration) to chromium, cadmium, and copper, and was more reliable (lower in terms of coefficient of variation) than those for frond area. Compared to conventional Lemna-based tests, the S. polyrhiza test is easier to perform (requiring only one 24-well plate, 3 mL of medium and a 72-h exposure). Moreover, it does not require livestock cultivation/maintenance, making it more suitable for repeated measurements. Measurements of S. polyrhiza root length may be suitable for assessment when copper and chromium in municipal and industrial wastewater exceed the environmentally permissible levels.

Automated summary

This study investigated the use of greater duckweed as a bioindicator of metal pollution. The plant showed significant differences in response to different metals, with silver being the most toxic and copper being the least toxic. Additionally, root growth was found to be more sensitive and reliable compared to frond size. The greater duckweed test is easier to perform and does not require livestock cultivation/maintenance, making it suitable for repeated measurements. Measuring the root length of greater duckweed may be a suitable method for assessing copper and chromium levels in wastewater.