Undergraduate Honors Thesis Projects

Date of Award

Spring 2023

Document Type

Honors Paper

Degree Name



Biology & Earth Science


Dr. Jeffrey Lehman

First Committee Member

Dr. Jeffrey Lehman

Second Committee Member

Dr. Brandon Sinn

Third Committee Member

Dr. Michelle Acker


Duckweed, Lemna minor, Calcium Oxalate Crystals, Heavy Metals

Subject Categories

Biology | Botany | Other Plant Sciences | Plant Biology


Lemna minor L., duckweed, is a common aquatic plant used for the phytoremediation of wastewater. Heavy metal contamination poses a significant issue, and numerous studies have been conducted on the efficiency of L. minor’s hyperaccumulation ability of these metals. Calcium oxalate crystals are an important aspect of the growth and development of L. minor, but how they are influenced by the uptake of heavy metal has not been extensively studied. This study aims to determine the effects that lead, cadmium, and copper have on the formation of calcium oxalate crystals, vegetative growth, and chlorophyll a and b content on L. minor. Cultures were grown in a diluted Hoagland’s nutrient solution for thirteen days in various concentrations of lead (0, 50, 100, 200 and 300 mg/L), copper (0, 5, 10, and 30 mg/L), and cadmium (0, 5, 20, 35, and 50 mg/L). Samples were collected on days 1, 5, 8, and 13 and analyzed for plantlet number, plantlet fresh weight, frond area, chlorophyll a, b, and ab, and crystal density, size, and number with polarized light microscopy and a spectrophotometer. It was determined that higher concentrations of heavy metals impact the overall growth and photosynthetic capacities of L. minor, which are indicators of its toxicity. Additionally, crystal formation was significantly impacted (i.e., crystal size was reduced by 78%, 51%, and 56% for lead, copper, and cadmium) at higher concentrations of heavy metals, indicating calcium sequestering is greatly inhibited and reduced. This contributes to a further understanding of the phytoremediation capabilities of L. minor and its tolerance to heavy metal toxicity.

Licensing Permission

Copyright, all rights reserved. Fair Use

Acknowledgement 1


Acknowledgement 2