Contribution of transformation products towards the total herbicide toxicity to tropical marine organisms

Philip Mercurio,Matt Kenway,Florita Flores,Andrew P Negri,Jochen F Mueller,Victor Beltran,Stephen Parks,Geoff Eaglesham

doi:10.1038/s41598-018-23153-4

Abstract

The toxicity of herbicide degradation (transformation) products is rarely taken into account, even though these are commonly detected in the marine environment, sometimes at concentrations higher than the parent compounds. Here we assessed the potential contribution of toxicity by transformation products of five photosystem II herbicides to coral symbionts (Symbiodinium sp.), the green algae Dunaliella sp., and prawn (Penaeus monodon) larvae. Concentration-dependent inhibition of photosynthetic efficiency (∆F/Fm′) was observed for all herbicides in both microalgal species. The toxicity of solutions of aged diuron solutions containing transformation products to Symbiodinium sp. and Dunaliella sp. was greater than could be explained by the concentrations of diuron measured, indicating transformation products contributed to the inhibition of ∆F/Fm′. However, the toxicity of aged atrazine, simazine, hexazinone, and ametryn solutions could be explained by the concentration of parent herbicide, indicating no contribution by transformation products. Prawn larval metamorphosis was not sensitive to the herbicides, but preliminary results indicated some toxicity of the transformation products of atrazine and diuron. Risk assessments should take into account the contribution of herbicide transformation products; however, further studies are clearly needed to test the toxicity of a far wider range of transformation products to a representative diversity of relevant taxa.

Highlights

Tropical marine ecosystems are highly diverse and support many vulnerable and protected species including corals, seagrass, dugong, and sea turtles
In order to evaluate the potential contribution of toxicity by known and unknown transformation products of five Photosystem II (PSII) herbicides we compared the acute toxicity of partially aged PSII herbicides with their parent compounds[36]
All ICXs of the aged diuron solutions were lower for Symbiodinium sp., as were the IC10s and IC20s for Dunaliella sp., indicating additional contribution to toxicity by transformation products

Summary

Introduction

Tropical marine ecosystems are highly diverse and support many vulnerable and protected species including corals, seagrass, dugong, and sea turtles. Microalga common in tropical estuaries were less sensitive to 3,4-DCA and DEA than their parent herbicides[16], adding to the ambiguity regarding contributions of herbicide transformation products to total toxicity[36]. The combined contributions of parent compounds and transformation products have been included in some overall risk assessments[37,38,39], but this is not a commonly applied approach. In order to evaluate the potential contribution of toxicity by known and unknown transformation products of five PSII herbicides we compared the acute toxicity of partially aged PSII herbicides (including transformation products) with their parent compounds[36]. The toxicities of parent and aged pesticides were compared using relevant tropical marine photosynthetic organisms (i) the coral symbiont (Symbiodinium sp.) and (ii) the green algae Dunaliella sp. The toxicities of parent and aged pesticides were compared using relevant tropical marine photosynthetic organisms (i) the coral symbiont (Symbiodinium sp.) and (ii) the green algae Dunaliella sp. and a non-photosynthetic organism (iii) prawn (Penaeus monodon) larvae

Methods

Results

Conclusion