Resting egg banks can facilitate recovery of zooplankton communities after short exposure to glyphosate.

We assessed the short-term viability and recovery of zooplankton communities after exposure to glyphosate (active ingredient-a.i.). We conducted a hatching experiment in two steps: Step 1-natural lake sediments containing resting egg banks were placed into individual trays and exposed to a solution medium of glyphosate at three different treatments (LD = Values below the detection limits, LD < 0.05, 0.44, and 0.89 mg a.i./L) for 14 days; and Step 2-we replaced the exposure solution of glyphosate with distilled freshwater, keeping them all trays under freshwater conditions for another 14 day. The results from Step 1 showed significant effects of glyphosate on the emergence patterns of resting eggs, with a reduction in hatching of rotifers, mainly at concentrations of 0.44 and 0.89 mg a.i./L. On the other hand, the results from Step 2 showed an increase in the emergence of viable eggs for rotifers after restoration of freshwater conditions in all treatments; there was no effect for total zooplankton and microcrustaceans. These findings suggest that (i) glyphosate may, effectively, impair zooplankton hatching from resting egg banks; (ii) the magnitude of the negative effects depends on the the zooplanktonic group considered; and (iii) the restoration of freshwater conditions may, in some way, allow the recovery of the zooplankton community from viable egg banks. Our results can be useful in predicting the influence of glyphosate on the distribution patterns of freshwater zooplankton, which can represent vital information for environmental managers.

Mixture of commercial herbicides based on 2,4-D and glyphosate mixture can suppress the emergence of zooplankton from sediments.

It is generally assumed that zooplankton can recolonize lakes that have been exposed to pesticides, via their dormant egg banks. Hitherto, few studies have evaluated the relative importance of dormant egg bank recruitment in the re-establishment of zooplankton communities in the presence of pesticide. This study investigated the effects of commercial products Bratt® (a.i. 2,4-D), Roundup® (a.i. glyphosate) and their mixture on the emergence (abundance and taxon richness) of dormant zooplankton egg banks from natural lake sediment. Sediment samples were collected from the surface sediment (<10 cm depth) in four lakes in Southeast São Paulo, Brazil. We performed a hatching experiment, in which natural lake sediments containing dormant eggs were exposed separately to Bratt® (applied concentrations ranging from 0.30 to 20 mg L-1), Roundup® (0.28-8.5 mg L-1), and combined mixtures of all concentrations, plus one control (non-exposure to formulated herbicides) for a period of 28 days. All tested concentrations of Bratt®, Roundup® and their mixture reduced the abundance and taxon richness of emerging zooplankton (except 2 mg L-1 of Bratt®). This effect was more pronounced in rotifers. In comparison, there were no negative effects on the emergence of microcrustaceans. These findings suggest that commercial products Bratt®, Roundup® and their mixture can suppress the emergence of rotifers, thereby influencing zooplankton recruitment potential in lakes impacted by the presence of these commercial herbicides. Our results stress the importance of the need for additional studies to assess the effects of pesticides on dormant egg banks.