Can duckweed be used for the biomonitoring of textile effluents?

Abstract

In certain countries, it is important to monitor for poorly managed freshwaters in order to avoid ecosystem degradation. This can be achieved through biomonitoring involving the use of living organisms as ecological alert indicators. In this context, biotests of the duckweed Lemna gibba (L. gibba) were undertaken to assess the toxic effects of pollutants from the textile industry on a natural ecosystem. L. gibba was exposed to different concentrations (5–100 mg/L) of two dyes, namely Direct Red 89 (DR-89) and Vat Blue 20 (VB-20), under laboratory conditions. Our findings showed that at dye concentrations > 50 mg/L, visible damage to the duckweed (chlorosis and disconnection of fronds, leading to severe necrosis) appeared from the third day of toxicity testing due to the toxicity of the dyes. However, at dye concentrations ≤ 50 mg/L, the duckweed showed no visible signs of toxicity within an exposure time of 4 days, although these concentrations did significantly reduce the growth rate of L. gibba and its photosynthetic pigment levels. The dye concentration that reduced the growth rate of the plant by 50% (IC50) was 36.3 mg/L for DR-89 and 26.9 mg/L for VB-20. The dye-concentration-dependent reductions in the growth and photosynthetic pigment levels of the duckweed demonstrated that this plant would be sensitive to the concentrations of these dyes in aquatic systems. The current findings therefore prove that physiological alterations occur in L. gibba following dye exposure, suggesting that this species is highly suited to use in the biomonitoring of textile effluents that contaminate water bodies.