The impact of common herbicides in Tagus estuary ecosystem may be higher than expected

Abstract

Introduction: Artemia spp. (Crustacea, Branchiopoda) is commonly used in aquaculture as a live feed for fish and crustaceans, as well as in toxicological studies of new chemicals in the aquatic environment [1]. In the wild, Artemia spp. occurs in saline areas, such as Salinas do Samouco - Alcochete, in the Tagus estuary, being a primary part of a large ecosystem [2]. A recent study showed the toxic effect of glyphosate, the active principle of several herbicides, on this organism [3]. This study aimed to investigate the effect on Artemia of three herbicides freely sold in Portugal.

Materials and methods: Artemia cysts were hatched into nauplii after 16-18h at 26ºC, under day illumination, aeration being strong and continuous [1]. Ten nauplii were randomly collected for each vessel test, performed at 26°C in 100 mL of artificial seawater with 35 ppt of salinity, aeration of 5 mL/s, under 2000 lux illumination [3]. The assays were made in duplicate. The mortality of the naupliis was measured after 4, 16, 20, 24 and 48 hours exposure to 0.1 ppm of the herbicides Natria, Resolva and Roundup (10 µL/100mL), along with the control group. The mortality of the naupliis was measured after 24 and 48 hours exposure to 0.05 and 0.1 ppm of the 3 herbicides, along with the control group. Kit aquarium tests for pH, NH₄, NO₃, and NO₂ were applied to the contents of the vessels after 0, 24 and 48 hours of toxicological testing.

Results: The mean of 4 assays indicated that the time required to kill 50% of the organisms exposed to 0.1 ppm of herbicides Natria, Roundup and Resolva was 11h, 14h and 40h respectively (Figure 1). The reduction to 0.05 ppm of the Natria and Roundup herbicides maintained Artemia mortality higher than 50% in 24 hours of exposure. Ammonium kit tests showed no relevant difference between vessel control and vessels with herbicides.

Figure 1. Effect of herbicides at 10 µL/100 mL along 4, 16, 20, 24 & 48h.

Discussion and conclusions: Both Natria and Roundup herbicides showed acute toxicity to Artemia. The toxicity of the Roundup active ingredient (glyphosate) is known [3] but the active ingredients of Natria (octanoic and decanoic acids) are not considered to be toxic and are easily sold in Lisbon and around. The indiscriminate use of Natria can lead to large discharges into the Tagus river and have consequences for the Artemia and its trophic chain, as the scyphozoan Catostylus tagi. It is worrying that aquarium tests for ammonia have not been able to detect Natria at toxic concentrations, although it is composed of ammonia salts.

Acknowledgements

This study was funded by Egas Moniz Coop Ensino Superior CRL, project EM-ZM 03/04.