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Water-sediment Glyceria maxima toxicity test

The EFSA Guidance on tiered risk assessment for edge-of-field surface-waters (2013) necessitates the testing of Glyceria maxima for special cases. This study determines the effects of a test item on the vegetative growth or increase in biomass of G. maxima. Despite the fact that G. maxima testing is quite a new requirement, ibacon has already performed many such studies and is experienced with this species. Aquatic plants found in static water bodies may experience prolonged or continuous exposure to chemicals as well as repeated exposures. Therefore we offer not only the required dose-response design, but also recovery designs with the ability for the plants to recover from the treatments and pulsed exposures . These scenarios can be simulated by static or static renewal systems. 

Study Design

Test organisms

The reed sweet grass G. maxima grow as an emergent monocotyledon. It is found as a pure, dense colony in permanently or seasonally flooded areas over nutrient-rich substrates. New plants develop predominantly by vegetative spread of rhizomes. However, these plants are not easy to cultivate. That is why plants are obtained by commercial breeders during spring and summer times.

 

Course of the test

Essentially a ring-test is conducted in order to develop a guideline for G. maxima testing. The general procedure is comparable to the water-sediment toxicity test with M. spicatum.

Before test start the plants have to be kept under test conditions (16:8 light/dark ratio, high light intensity, 22 ± 2°C) to adapt the plants. One single plant is introduced into a small pot containing artificial sediment and is exposed in a vessel with reconstituted test media (Smart and Barko). The test medium should cover the sediment surface by at least 3 cm. Each test should consist of a geometric series of test concentrations with four to five replicates and an untreated control with six to eight replicates. 

After the acclimatization phase plants with 3-4 leaves can be used as test plants. The test substance is applied via the test media or via the artificial sediment and during the 21 days of exposure normally no water exchange is conducted. If the test item degrades fast a semi-static approach can be conducted.

At test start and test termination shoot length and biomass are determined.

Endpoints

The endpoints of the study are the increase in shoot height (including newly developed shoots) as well as fresh and dry weight. Based on these parameters NOEC, LOEC and EC50 (EC20, EC10) can be calculated for yield and growth rate. Moreover sublethal effects, such as growth abnormalities or necrosis are determined.

Guidelines and Literature

  • Davies, Jo (2001): Guideline for Assessing the Effects of Pesticides on the Growth of Glyceria maxima, Bristol, United Kingdom, May, 23, 2001.
  • EFSA Guidance on tiered risk assessment for plant protection products for aquatic organisms in edge-of-field surface waters. EFSA Journal 2013; 11 (7): 3290.
  • Ring-test protocol for evaluating the effects of chemicals on Glyceria maxima in a water-sediment system, September 2016.