Acute toxicity of four metals to three tropical aquatic invertebrates: The dragonfly Tramea cophysa and the ostracods Chlamydotheca sp. and Strandesia trispinosa.

The relatively low availability of toxicity data for indigenous tropical species has often been discussed. In addition, several taxonomic groups of invertebrates are understudied, such as dragonflies and ostracods. The aim of the present study was therefore to evaluate the acute toxicity of four metals (cadmium - Cd, copper - Cu, manganese - Mn, and mercury - Hg) to the tropical dragonfly nymphs of Tramea cophysa and two tropical ostracod species (Chlamydotheca sp. and Strandesia trispinosa). Toxicity data for other invertebrates were also mined to allow comparing the sensitivity of the three test species with that of other (temperate and tropical) invertebrates. The order of metal sensitivity was different for the three test species: T. cophysa: Cu > CdHg > Mn, Chlamydotheca sp.: Cd > Cu > Hg > Mn, and S. trispinosa: Cd > Hg > Cu > Mn. However, manganese was the least toxic metal tested for all three species, which is hypothesized to be due to a possible metal transfer to the cuticle of the moulting test species. The sensitivity ranking of the three test species to the metals was S. trispinosa > Chlamydotheca sp.>T. cophysa (except for Cu for which the ranking was Chlamydotheca sp.>T. cophysa > S. trispinosa). Overall, the test species are concluded to be suitable test organisms for tropical toxicity evaluations. Future studies should also evaluate the chronic toxicity and include other important metal exposure routes such as sediment and food.