MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(GOO-1117-634649) Factors influencing the exchange of water between in situ exposure chambers and the surrounding environment.

Goodson, R¹, Ingersoll, C², Wang, N², ¹ Westminster College, Fulton, MO, USA² US Geological Survey, Columbia, MO, USA

ABSTRACT- The objective of this study was to evaluate the factors that may influence the exchange of water between in situ exposure chambers and the surrounding environment. In situ exposure chambers have been developed to expose aquatic invertebrates, fish, or amphibians to contaminated water or sediment in the field. Chambers were constructed out of PVC materials to contain 450 ml of water. Mesh used in the current study was 75-, 150- or 300-um stainless steel screen. A solution of 450 ml of well water containing dye (red 40 food coloring) was placed in each chamber. Individual chambers were placed in 40-L buckets containing 10 L of well water and absorbance was recorded inside or outside chambers at 0, 24, 48, 72, and 96 h. Four laboratory studies were conducted to evaluate exchange of water between chambers and the surrounding environment: (1) mesh size; (2) fouling (conditioned chambers for 48 hours in biologically-active water); (3) fouling with aeration of the surrounding water, and (4) placement of chambers in sediment. A fifth study was conducted by placing chambers in an experimental stream in sediment or in water. In the laboratory studies, water in chambers with 300-um mesh equilibrated with the surrounding environment within about 24 h; however, chambers with 75-um mesh did not reach equilibrium within 96 h. Fouling of the mesh delayed time to equilibration by 24 to 48 hours in the chambers with 75- and 150-um mesh. Gentle aeration of water in the buckets surrounding chambers with fouled mesh resulted in equilibration within 24 hours for all mesh sizes. Placement of chamber in sediment resulted in only 40 to 50% water change by 96 h across all mesh sizes. Chambers placed in water in an experimental stream reached equilibrium within 24 h (similar to the aeration treatment in the laboratory). Chambers placed in sediment in an experimental stream resulted in only limited water exchange by 96 h across all mesh sizes (similar to the sediment treatment in the laboratory). Results of these studies suggest there may be adequate exchange of water when chambers with larger mesh size are placed in water. However, chambers with smaller mesh size or chambers placed in sediment may severely limit exchange of water and may not adequately represent exposure conditions in situ.

Key words: in situ toxicity, exposure chamber, sediment toxicity, water toxicity