Simultaneous Control of Phenanthrene and Drought by Dual Exposure System: The Degree of Synergistic Interactions in Springtails was Exposure Dependent

Abstract

Organisms in the environment are exposed to multiple stressors. However, for terrestrial invertebrates, it remains difficult to study the effects of combined stressors under well-defined exposure conditions. Thus, the current study develops a new dual exposure system for the simultaneous and independent control of chemical and drought exposure in bioassays with terrestrial organisms: Passive dosing from silicone controlled the chemical activity of phenanthrene (chemical stress), while saline solutions controlled the water activity (drought stress) in the closed exposure system. The dual exposure system was then applied in a full factorial experiment with seven exposure levels (7(2)), which aimed at determining the combined effects of phenanthrene and drought on the survival of the terrestrial springtail Folsomia candida after 7 d exposure. Fitting an "independent action" model to the complete data set revealed statistically significant synergy between phenanthrene and drought (p < 0.0001). However, the degree of synergy was exposure dependent with some synergy at higher and only minor synergy at lower exposure levels. This emphasizes the need for taking exposure levels into account when extrapolating synergy observations from (eco)toxicological studies done at high exposure levels.

Recovery period of Folsomia candida influence the impact of nonylphenol and phenanthrene on the tolerance of drought and heat shock

“…It seems that both NP and PHE might destabilize the cell membrane, decreasing its ability to cope with the increased fluidity associated with increasing temperature (van Dooremalen and Ellers, 2010). The evidence of a general destabilization by these chemicals is further supported by the fact that they both have been found to interact synergistically with desiccation stress in Folsomia candida (Højer et al, 2001;Holmstrup et al, 2014b;Schmidt et al, 2014). Besides destabilizing the cell membrane, NP and PHE may affect the cell in a number of ways, which might act in synergy with the natural stressors.…”

“…The contents of PHE in springtail tissues was determined after extraction in acetonitrile followed by GC-MS analysis as described in details by Holmstrup et al (2014). The contents of NP was determined after extraction in 70% ethanol followed by glycation, solid phase extraction and finally analysis by GC-MS.…”

“…The contents of NP was determined after extraction in 70% ethanol followed by glycation, solid phase extraction and finally analysis by GC-MS. The details of the analytical methods are described elsewhere (Holmstrup et al 2014).…”

“…The present study may hence potentially underestimate the degree of synergy, since the stressors were only applied individually, sequentially, and not simultaneously. Schmidt et al (2014), showed an exposure dependent synergy between drought and PHE when exposing Folsomia candida to the two stressors simultaneously instead of sequentially by using silicone plates to control the chemical activity and saline solutions to control drought stress. They found that the degree of synergy was exposure dependent with some synergy at higher-and only minor synergy at lower exposure levels.…”

“…Synergistic interactions between naturally occurring stressors and several toxic substances have already been established (Højer et al, 2001;Sørensen and Holmstrup, 2005;Skovlund et al, 2006;Schmidt, 2014;Sjursen et al, 2001a;Slotsbo et al, 2009). Slotsbo et al (2009), for example, found a highly significant reduction of the heat tolerance in springtails after exposure to sublethal concentrations of mercury.…”