An in Situ Bioassay for Estuarine Environments Using the Microalga Phaeodactylum Tricornutum

Abstract

This study aimed at evaluating the potential of an in situ algal bioassay for routine toxicity estimates of potentially contaminated estuarine environments using the microalga Phaeodactylum tricornutum immobilized in alginate beads. The influence of the initial cell density in the beads and of salinity on algal growth was first investigated. The potential of the proposed bioassay was evaluated by comparing laboratory with in situ results. A good growth performance of P. tricornutum was observed at all starting densities of beads. Although the growth rate of P. tricornutum was significantly affected by salinity, acceptability criteria currently adopted in algal assays were met, indicating the suitability of P. tricornutum as a test species for bioassays in estuaries. The large differences observed between the laboratory and in situ responses of P. tricornutum were most probably due to the temperature and light conditions less favorable for algal growth in the field and to the lack of representativeness of water samples compared to the field fluctuating conditions. These results showed the need for in situ assessments, especially in estuarine environments influenced by tides. To a lesser extent, the bioassay itself may also have been responsible for the laboratory and field differences. Further improvements in the bioassay chambers and procedures were also discussed.

Optimization of growth conditions for laboratory and field assessments using immobilized benthic diatoms

“…Algal cells were immobilized by encapsulation in beads of calcium alginate 1.3 and 1.5 % (w/v) concentrated, following the protocol suggested by Moreira-Santos et al (2002) and Bozeman et al (1989). Solutions of 1.3 and 1.5 % (w/v) sodium alginate (CAS no.…”

“…9005-38-3) were prepared with sterilized distilled water. Since the initial cell density is critical for the viability of immobilized cells because of nutrient availability, carbon dioxide diffusion and light penetration (Moreira-Santos et al 2002), we tested two initial cell densities: 10 4 and 10 5 cells mL −1 . They were established considering previous studies (e.g.…”

“…The immobilization of the diatoms in encapsulation matrices offers many advantages over the use of free cells, especially for in situ toxicity assessment as stated by Araújo et al (2010). The encapsulation of microalgae has been successfully used in toxicity tests developed for application in freshwater (Moreira-Santos et al 2002;Moreira-Santos et al 2004b), estuarine and marine ecosystems (Moreno-Garrido et al 2003, 2007.…”

“…As such, the effect of different conditions on N. libonensis growth was assessed by testing: (i) different incubation temperatures (23 and 15°C) and (ii) photoperiods (24 L and 12 L :12 D ), which were both variables set considering standard laboratorial conditions and field scenarios; (iii) different initial cell density (10 4 and 10 5 cells mL −1 ), which was already proven to affect the test outcome in other species (Moreira-Santos et al 2002;MorenoGarrido 2008); (iv) cell immobilization in matrices with two distinct alginate percentages (1.3 and 1.5 %), thus addressing the effect of alginate concentration in exposure and encapsulation efficiency, versus free cells; (v) different test periods (T6, T9, T11), hence evaluating whether longer periods-generally required in tests run in the field due to variation in photoperiod and temperature-suit the species physiology and/or allow better detection of effects. The ecotoxicological response of N. libonensis under these conditions was still validated with the testing of reference chemicals (potassium dichromate and 3,5-dichlorophenol) in artificial medium (Chu 10) and in natural stream water (sample taken from a reference stream in Luso, Portugal; Silva 2008).…”

Estudos limnológicos e ecotoxicológicos com amostras de água e sedimento do ribeirão Limeira - Piquete/Lorena-SP

“…fitoplâncton (CULP et al, 2000;MOREIRA-SANTOS, 2002, 2004a, 2004b, anfípodos (CHAPPIE; BURTON, 1997;MALTBY et al, 1990), cladóceros (LOPES et al, 2007;PEREIRA et al, 2002 ), peixes (CASTRO et al, 2004;MOREIRA et al, 2010;SMOLDERS et al, 2004), quironomídeos (CASTRO et al, 2003;CHAPPIE;BURTON, 1997;CONRAD et al, 1999;FARIA et al, 2008;SOARES et al, 2005; WARREM, entre a exposição e os efeitos são mais complexos (CLEMENTS; KIFFNEY, 1994;PEREIRA et al, 1999;. CHERRY et al, 2001).…”