Annika Agatz, PhD project, University of York, UK
Contact: Enable-Javascript@To-Read-E-mail-Address
Summary of outcomes
The improvement of methods enabled testing of some important hypotheses with the overall aim to better understand sub-lethal effects and the relative importance of such impacts at the population level. This project identified some rather subtle behaviours that were previously unknown, improved the knowledge on some key questions and opened some additional uncertainties for environmental risk assessment. The conducted work shows the potential of making effect assessment more environmentally-realistic to allow the risk assessment to move towards the reduction of false positive and false negative assessments.
Background
Great effort is made by different stakeholders (industry, regulators, academia and decision makers) to predict, understand and evaluate the fate and effects of plant protection products (PPPs). This procedure is called the environmental risk assessment (ERA). The aim is to protect the environment against impacts with adverse consequences for environmental and human health. Despite these efforts, several examples of PPPs exist where unacceptable impacts have been observed after the regulated use of those substances in the environment. Cases such as these indicate the need to improve the risk assessment procedures to prevent false positive assessment. However, making the assessment more conservative would neglect the benefits of PPPs. Thus, the risk assessment needs to be improved to be protective in all cases but not over-protective.
Several scientific committees of the European commission (SCHER, SCENHIR, SCCS) have recently developed a list of relevant research needs to be addressed in order to improve the risk assessment of PPPs. Overall, this list addresses the need of improving the risk assessment towards being more environmentally-realistic.
Feeding was chosen as the main endpoint of interest for this project because alteration in feeding can potentially disturb ecosystem function via effects onto the population level and ecosystem processes (protection goals for ERA). Furthermore, feeding has frequently been shown to be affected at low concentrations (i.e., more environmentally-realistic).
Aims
1) Assessing the feasibility of long-term feeding assays with aquatic invertebrates to investigate effects of time-variable exposure.
2) Assessing the consequences of such impacts under natural stress to individual traits of aquatic invertebrates.
3) Assessing the impact of such impacts under additional anthropogenic stress for populations.
Model species and model substances
Specific attention was on the aquatic invertebrates Daphnia magna and Gammarus pulex as model species and two PPPs (imidacloprid and carbaryl) as model substances.
Objectives
1) Development of feeding assays with two aquatic invertebrates (Gammarus pulex and Daphnia magna) focusing on the measurement at a daily resolution.
2) Explore the concentration-dependent impact of two pesticides (imidacloprid and carbaryl) on the feeding rate of both species.
3) Assess the feasibility of measuring consequences of pesticide-induced feeding inhibition on growth and reproduction for both species when using the experimental method developed in objective 1.
4) Investigate the transposition of toxicant-induced feeding inhibition on growth and reproduction for one of these species under differing food availability for the test organisms.
5) Explore whether impacts observed in objective 4 are direct effects of the pesticide or derive from acclimation to feeding inhibition.
6) Conducting a population experiment with Daphnia magna to explore the effect of short-term feeding inhibition from pesticide exposure to populations.
7) Explore whether result of objective 6) can be predicted from result of objective 4.
Main experiments conducted
| Test | Experimental explanation | Question(s) addressed | Get details |
| 1 | The effect of parasite infection and food quality to the feeding rate of Gammarus pulex | Does acanthocephalan parasite infection and food quality have an effect on the feeding activity? | Variability in feeding of Gammarus pulex: moving towards a more standardised feeding assay |
| 2 | The effect of body mass to the feeding rate of individual Gammarus pulex | Is the feeding rate size dependent? How strong are the differences and the fluctuations over time? | Variability in feeding of Gammarus pulex: moving towards a more standardised feeding assay |
| 3a | The effect of imidacloprid to the individual feeding rate, of good fed and not infected Gammarus, over time. The experiment includes a recovery phase. | What concentration causes an effect on the feeding activity? Is the effect reversible, time and concentration dependent? Is the feeding rate in the control stable over time? | Imidacloprid perturbs feeding of Gammarus pulex at environmentally-relevant concentrations. |
| 3b | The effect of carbaryl to the individual feeding rate, of good fed and not infected Gammarus, over time. The experiment content an exposure and recovery phase | Same as 3a | On request |
| 9a | The effect of starvation to the individual feeding rate, of good fed and not infected Gammarus, over time. The duration of starvation is 1,2,3 and 4 days | What happened with the feeding rate after different durations of starvation? | On request |
| 10 | Measuring the effect of imidacloprid to Gammarus pulex at different lipid contents | Does the lipid content of Gammarus pulex change within 3 weeks of feeding with different food sources? Is the toxicity of Imidacloprid to the feeding rate different when the lipid content of the organisms is different? | On request |
| 11 | Measuring the C-N ratio of Gammarus, fungi and different leaf types (whole leaves and the veins separately) | Can the differences in the feeding rate for different food sources be explained by differences in the C-N ratio? | Variability in feeding of Gammarus pulex: moving towards a more standardised feeding assay |
| 12 | Acute toxicity test of imidacloprid to D. magna for 8 days. Test starts with neonates | Which concentration should be used to see effects on reproduction without having mortal effects? Is the EC50 (48h) from the literature comparable with the EC50 generated when fed the organisms during the test? How does the effect looks like when observed over a longer period than usually (OECD test) | Feeding inhibition explains effects of imidacloprid on the growth, maturation, reproduction and survival of Daphnia magna. |
| 13 | The effect of imidacloprid exposure in the early life stage of D. magna. | Is the reproduction of D.magna affected when exposed in the juvenile development? | Feeding inhibition explains effects of imidacloprid on the growth, maturation, reproduction and survival of Daphnia magna. |
| 15 | Influence of imidacloprid to the feeding activity of D. magna | Is the lower growth rate observed in experiment 12 caused by a lower feeding rate? Which concentrations of imidacloprid affect the feeding activity of D. magna? | Feeding inhibition explains effects of imidacloprid on the growth, maturation, reproduction and survival of Daphnia magna. |
| 22 | The effect of imidacloprid exposure in the early life stage of D. magna and the development of their offspring | What happens with the F1 of Daphnia when mothers were exposed to imidacloprid during their juvenile development? Do we see any differences in their reproduction and growth compared to the offspring of not exposed mothers? | On request |
| 23 | Acute toxicity of carbaryl to neonates, juveniles, primipara and adult D. magna. Organisms of all age groups were either starved or fed prior exposure. | Does the feeding history determine the effect intensity? | On request |
| 29 | The influence of short-term feeding inhibition due to imidacloprid exposure on D. magna populations. | What happens with the population under single, multiple and mixture exposure to imidacloprid and carbaryl. | Evidence for links between feeding inhibition, population characteristics and sensitivity to acute toxicity for Daphnia magna. |
Important findings
Feeding assays with G. pulex are able to reveal impacts of PPPs at environmentally-relevant concentrations. Including the measurement of recovery potential is important because compensational feeding after exposure indicates impacts at even lower levels of exposure. The developed method requires further improvement to enable long-term experimentation.
Short-term impacts on feeding of D. magna can cause severe impacts at the individual and population level.
A direct extrapolation from D. magna feeding assays to influences at the higher level of organisation was observed to be impossible. The transposition of altered feeding due to PPPs was found to depend not only on food availability at the time of exposure but also on the reproductive strategy the individual follows. Both factors were found to be more flexible under multiple stresses than has been reported in the literature.
Publications
Agatz A. & Brown C.D. (2014). Variability in feeding of Gammarus pulex: moving towards a more standardised feeding assay. Environmental Sciences Europe 2014, 26:15 doi:10.1186/s12302-014-0015-4
Agatz et al. (2014) Imidacloprid perturbs feeding of Gammarus pulex at environmentally-relevant concentrations. Environmental Toxicology and Chemistry 33(3): 648-653.
Agatz A. & Brown C.D. (2013). Evidence for links between feeding inhibition, population characteristics and sensitivity to acute toxicity for Daphnia magna. Environmental Science and Technology 47:9461−9469.
Agatz et al. (2013). Feeding inhibition explains effects of imidacloprid on the growth, maturation, reproduction and survival of Daphnia magna. Environmental Science and Technology 47:2909–2917.
Agatz et al. (2012). Promoting effects on reproduction increase population vulnerability of Daphnia magna. Environmental Toxicology and Chemistry 31(7):1604-1610.
Oral presentations
„Impacts of imidacloprid on individual performance and population dynamics of Daphnia magna“, SETAC Europe Annual Meeting, 2013, Glasgow, UK
„Using an IMB as virtual laboratory for data interpretation – an example of model application“, CREAM open conference, 2013, Leipzig, DE
„Sub-lethal effects of imidacloprid pulses to aquatic invertebrates”, SETAC World Congress, 2012, Berlin, DE
„Effects of imidacloprid and carbaryl on the individual feeding activity of Gammarus pulex (L.)“, SETAC Young Environmental Scientists Meeting, 2011, Aachen, DE
“Effects at a daily resolution of imidacloprid on the individual feeding activity of Gammarus pulex (L.)”, SETAC Europe Annual Meeting, 2011, Milan, IT
“Feeding inhibition of Gammarus pulex; what happens with the control?”, CREAM open mid-term meeting, 2011, Krakow, PL
Supervisor: Colin Brown (University of York)
Co-supervisor: Roman Ashauer (Eawag)
Associated partner: CRD
Last updated: 23-03-2014
