Effects of light intensity and population density on duckweed systems exposed to pesticides: toxicity and phytoremediation

Area of Science:

• Environmental Chemistry
• Plant Physiology
• Ecotoxicology

Background:

• S-metolachlor and atrazine are prevalent freshwater contaminants.
• Pesticide impacts on aquatic plants require further investigation.

Purpose of the Study:

• To evaluate the effects of light intensity, plant density, and herbicide concentration on duckweed (S. polyrhiza).
• To assess the influence of these factors on duckweed growth, physiology, and phytoremediation capacity for S-metolachlor and atrazine.

Main Methods:

• Greenhouse microcosm experiment over 12 days.
• Varied light intensity (100-400 μmol photons m⁻² s⁻¹), plant density (25-60%), and herbicide concentrations (S-metolachlor: 20-200 μg L⁻¹; atrazine: 15-150 μg L⁻¹).
• Measured growth, pigment content, photosynthesis, antioxidant system, and pesticide removal.

Main Results:

• Interactions between factors and herbicide concentration generally reduced photosynthetic capacity and growth rate.
• Duckweed exhibited higher survival with atrazine than S-metolachlor.
• S-metolachlor removal reached 76% and atrazine 59% at high density and environmentally relevant concentrations.
• Increased light intensity did not enhance phytoremediation; higher density improved total removal but reduced efficiency for S-metolachlor.

Conclusions:

• Duckweed physiology adjusts to pesticide stress via pigment and non-photochemical quenching increases.
• Phytoremediation potential of duckweed is influenced by environmental conditions and herbicide type.
• Findings support using duckweed in controlled systems for pesticide removal.