Controlled release experiments with nonylphenol in aquatic microcosms

Abstract

A method of controlled release of technical nonylphenol (tNP) was developed to simulate realistic exposure in ecotoxicological studies on aquatic organisms. The direct addition of tNP from an aqueous stock solution into 50 ml of water led to a concentration decrease of 80 to 90% weight/volume (w/v) from nominal values within 48 h. The inclusion of tNP in semipermeable low-density polyethylene (LDPE) lay-flat tubing (controlled-release devices [CRDs]) of different length allowed a continuous release into pure water at a rate of about 30 microg/cm2/d. Using CRDs in aquaria containing 15 L of 63-microm-filtered lake water, eight different concentrations with maxima between 38.1 and 326.7 microg/L were maintained for 11 d. During a second experiment in 15-L aquaria, five replicates of three concentrations were maintained using CRDs of the same length. Concentrations after 38 d varied between 0.1 and 6.7, 26.1 and 41.9, and 49.9 and 76.0 microg/L. In aquatic microcosms containing 230 L of lake water, a natural plankton community, 50 L of sediment, and macrophytes, seven different tNP concentrations (maxima 11-120.1 microg/L) were maintained over 45 d using CRDs of different length. They were replaced after 14 and 25 d because release of tNP was slower than predicted from laboratory experiments. Concentrations in the top 1-cm sediment layer were on average 19 times higher during the dosing period than concentrations in the water at the same time. In the sediments, different levels of applications led to concentrations that differed less distinctly than in the water. This method is suitable for exposing aquatic organisms continuously to constant, ecologically relevant concentrations of NP and represents an improvement over previous dosing methods in which exposure varied.

Effects of 4‐nonylphenol on phytoplankton and periphyton in aquatic microcosms

“…After the removal of the dosing devices, NP concentrations declined rapidly, reaching the detection limit within two weeks (Fig. 1) [12].…”

“…After a preapplication period of four weeks, microcosms were continuously exposed for six weeks (June 15‐July 30 1998) to different concentrations of technical NP (4‐NP > 98%, Sigma‐Aldrich, Seelze, Germany) using controlled release through low‐density polyethylene (LDPE) tubes (controlled‐release devices). The tubes had different lengths to achieve nominal NP concentrations of 40 (NP2), 100 (NP4), 130 (NP5), and 190 μg/L (NP7) [12]. During the first application week and the first week after the removal of the controlled‐release devices, NP concentrations were measured daily and at other times twice per week [12].…”

“…The tubes had different lengths to achieve nominal NP concentrations of 40 (NP2), 100 (NP4), 130 (NP5), and 190 μg/L (NP7) [12]. During the first application week and the first week after the removal of the controlled‐release devices, NP concentrations were measured daily and at other times twice per week [12]. Two microcosms were used as controls (k2, k3).…”

“…Effect concentration (EC50) and EC10 values were calculated by probit analysis ( p < 0.05). The NP concentration was analyzed following Pfister et al [12]. Measured NP concentrations at the beginning of the growth test were used for the calculation of effect concentrations.…”

Effects of nonylphenol on zooplankton in aquatic microcosms

“…Application of NP After a preapplication period of four weeks, technical NP (Sigma‐Aldrich, Seelze, Germany) was added to seven microcosms using controlled‐release devices made from semipermeable low‐density polyethylene (LDPE) tubes of different lengths [18]. The treatment lasted for six weeks.…”