Copper and chromium (III) uptake by duckweed

The duckweed Lemna minor was cultivated under laboratory conditions with the amount of incident light as limiting growth factor. The fronds were found to double every 3 days under the highest radiation intensity. The plants were exposed to Cu and Cr(III) solutions of 0.25 and 1.0 mg ℓ⁻¹ during 10 days. The plants needed to adapt for app. 8 days before attaining maximal, steady state removal. Cr(III) was removed more efficiently from the solution (75-100% in terms of concentration or load reduction) than Cu (35-40%), the higher efficiencies pertaining to the more dilute solutions. Uptake rates were 80-333 and 250-667 mg d⁻¹ m⁻² for Cu and Cr(III), respectively. The plants accumulated 1-2 g metal kg⁻¹ plant (dry weight) when exposed to the high concentration. Cu seemed toxic at 1.0 mg ℓ⁻¹, resulting in plant mortality after 8 days.