T11 AM Aquatic Plants: Methods, Mechanisms and Markers
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 343-344

(REI-1117-727426) Toxicity assessment for fluorinated organics using Lemna minor oxygen production.

Reinhold, D¹, Saunders, F¹, ¹ Georgia Institute of Technology, Atlanta, GA, USA

ABSTRACT- To determine the relationship between uptake and activity by L. minor at non-inhibitory to toxic concentrations of fluorinated organics, a novel oxygen-production assessment was developed and optimized. Assessment of O₂-production by L. minor was optimized to increase sensitivity and reliability of response while decreasing assessment time. Normalized O₂-production (M O₂/h-g L. minor) was measured in sealed reactors using manometers and partial pressure of gases with GC-TCD. Dark reactors were used to account for microbial and plant respiration. O₂-production by L. minor was negatively correlated with media pH and greater than 13 mM phosphate buffer was required to maintain neutral pH. Increasing carbonate concentration did not increase O₂-production by L. minor, indicating that media contained sufficient carbon for photosynthesis. Optimized O₂-production assessment allowed for easy quantification of L. minor activity under high-plant-density growth conditions similar to natural ecosystems. Toxicity studies using 24-h exposure and 6-h O₂-production assessment yielded toxicities similar to single-frond, 7-d chlorosis measurements. As such, O₂-production by L. minor was a viable, rapid alternative for assessing toxicity of contaminants in conjunction with uptake experiments. Uptake experiments with 10 M fluorinated organic yielded pseudo-first-order uptake rate coefficients of 0.2-0.7 d^-1, indicating 19-50% uptake from aqueous phase in 24-h. Uptake rate coefficients drastically decreased with increasing concentration of fluorinated organics at concentrations of 10-100 M. A gradual decrease in uptake rate coefficients was observed at concentrations greater than 100 M. Dependence of uptake rates on concentration did not correspond with toxicity. This presentation will illustrate the ability of aquatic plants to sequester contaminants, demonstrate independence of uptake on toxicity, and discuss methodology for sensitive toxicity assessment using L. minor O₂-production with reference to standardized duckweed toxicity assessments.

Key words: Lemna, fluorinated organics, uptake, oxygen production