The use of marine benthic diatoms in a growth inhibition test with spiked whole-sediment

Going with the flow: detection of drift in response to hypo-saline stress by the estuarine benthic diatom Cylindrotheca closterium

Avoidance response is a well-known mechanism for escaping environmental stress. For organisms with reduced active movement, such as benthic microalgae, drifting could be a specifically selected mean of avoiding less favorable environments. To test this hypothesis, a system was developed to assess if hypo-saline stress triggers drift in the estuarine benthic diatom Cylindrotheca closterium. Concurrently, the effects of salinity on growth inhibition were also investigated in order to compare the sensitivity of this endpoint with the drift response, and to estimate the immediate population decline caused by both drift and population growth responses. It was verified that the salinity value that inhibited the algal population growth by 50% (IGS₅₀) was 19, while the salinity value that triggered the drift response by 50% of the population (TDS₅₀) was 15. These results indicate that drift is an identifiable response triggered to escape stressful environments. The combination of the two responses (population growth and drift) showed that population decline based exclusively on the inhibition of population growth may result in an underestimation of the risk, compared with the decline when drifting to avoid stress is also taken into account.

Use of the microalgae Thalassiosira weissflogii to assess water toxicity in the Suape industrial-port complex of Pernambuco, Brazil

Microalgae are among the organisms that are most frequently recommended to assess water toxicity levels. They provide qualitative and quantitative population changes and have become important in environmental monitoring. The aim of the present study was to assess the sensitivity of the microalgae Thalassiosira weissflogii to water toxicity in the Suape industrial-port complex, and to potassium dichromate in the months of July, September and November of 2010 and January and September of 2011, as well as to compare the microalgae results to those obtained in tests with the sea urchin Lytechinus variegatus. The chronic toxicity tests with both species followed standardized methods. Once the exposure period was completed, the population increase of the algae was assessed using cell density and growth rate data and the percentage of L. variegatus pluteus larvae revealing normal and aberrant development was determined. The algal growth and percentage of pluteus results demonstrated that toxicity in the studied area varied according to the month. The present study confirmed that the best timeframe to conclude tests with the microalgae T. weissflogii was 72 h. The microalgae cell density results after 72 h were sufficient to assess the toxicity of surface water samples and were more sensible than the growth rates. The microalgae T. weissflogii was a sensitive test-organism for seawater toxicity.

Development and application of whole-sediment toxicity test using immobilized freshwater microalgae Pseudokirchneriella subcapitata

A method for a whole-sediment toxicity test using alginate immobilized microalgae Pseudokirchneriella subcapitata was developed using spiked sediments and applied to contaminated field sediment samples. For method development, a growth inhibition test (72 h) with algal beads was conducted for the sediments spiked with Cu or diuron. The method was validated by determining dose-response relationships for Cu and diuron in both fine-grained and coarse-grained sediments. The results of a spiked sediment toxicity test suggested that sediment particle size distribution (clay content) had a significant effect on the growth of P. subcapitata. The developed method using immobilized microalgae P. subcapitata beads was applied successfully in the toxicity test and toxicity identification evaluation (TIE) for the four field sediment samples. After a series of extractions with 0.01 M CaCl(2) solution, acetone, and dichloromethane, the extracted sediment, which was shown to be nontoxic to algae, was used as the control and diluent for the same sediment in the whole-sediment toxicity test. The results showed that all investigated field sediment samples were found to be toxic to the immobilized algae P. subcapitata, with their median effective concentration (EC50) values ranging from 41.4 to 79.0% after 72 h exposure. In the whole sediment TIE, growth of P. subcapitata was improved to varying degrees after adding zeolite, resin, or activated charcoal, suggesting different contributions to toxicity from ammonia, metals, and organic contaminants in the tested sediments.

Microphytobenthos in ecotoxicology: a review of the use of marine benthic diatoms in bioassays

Contamination in coastal zones is an increasing problem that adversely affects biological diversity and the functioning of coastal ecosystems. Sediment is an important compartment of these zones since large quantities of diverse contaminants can accumulate there. Whole-sediment toxicity assays are of increasing importance, and several assay methods using mainly invertebrates have been developed. However, an important part of the benthic community, the microphytobenthos (represented principally by benthic diatoms and cyanobacteria), has surprisingly been neglected. Recently, comprehensive studies have been conducted using benthic marine microalgae with the object of establishing a toxicity assay method for sediment samples. The main results published to date in the literature and obtained by our own team have been compiled and are discussed in this review. The value and feasibility of using certain organisms of the microphytobenthos group in ecotoxicology studies are also discussed, and a sediment quality guideline based on multivariate procedure has been derived from data obtained in previous studies. Finally, future perspectives for research in this field are discussed.