Background
Chemicals serve as the foundation of modern society, yet their ubiquity poses a significant threat to global biodiversity. This presentation explores how chemicals impact biodiversity from the molecular level through to the complex dynamics of entire ecosystems.
From Individual Organisms to Ecosystem Dynamics
The toxicological process begins with toxicokinetics—how a chemical enters, moves through, and is processed by an organism. While some substances are eliminated, others are biotransformed (sometimes becoming more toxic) or sequestered in tissues. Sequestration can lead to latency effects such as delayed toxicity, and trophic transfer resulting in secondary poisoning.
How a chemical causes harm, is toxicodynamics. The causal link between initial exposure and harm is mapped via the Adverse Outcome Pathway (AOP). This framework connects a "Molecular Initiating Event" (the chemical interacting with a receptor) to cellular and physiological responses, eventually resulting in adverse outcomes for growth, reproduction, and survival. Direct toxic effects on individual organisms can cause indirect effects on populations, communities and ecosystems that are mediated by species interactions.
Landscapes and Ecosystem Services
Chemical impacts are rarely confined to the point of origin. Due to the movement of mobile species, effects can spread across landscapes and systems—a phenomenon known as "action at a distance." Biodiversity loss directly impairs ecosystem functions and ecosystem services, including water purification, pollination, and natural waste disposal.
The Complexity of Mixtures and Regulation
In the natural world, organisms are seldom exposed to a single substance. Most chemicals act additively, but some exhibit synergism or antagonism. Mixtures can result in adverse impacts even when individual components are at "no-effect" levels. The so called "cocktail" or “something from nothing” effect. Chemical stressors also interact with environmental factors like climate warming, which can enhance toxicity.
Studying the effects of chemicals on biodiversity is a daunting task given the vast numbers of chemicals in use and species potentially exposed. Available ecotoxicity data is heavily skewed and dominated by a few "standard" species used in regulatory toxicity testing.
Future Directions in Predictive Ecotoxicology
To move beyond limited, single-species laboratory tests, the field is shifting towards predictive ecotoxicology. This involves:
Read-across and QSARs: Predicting the toxicity of new substances based on their chemical structure.
Effect Models: Extrapolating laboratory results to time-varying field exposures using toxicokinetic-toxicodynamic models, extrapolating to untested endpoints using mechanistic population and community models, and extrapolating to untested species using species sensitivity distributions and trait-based modelling approaches.
New Approach Methodologies (NAMs) and AOPs: Reducing animal testing while assessing risks across broader biological endpoints and species sensitivities.
Ultimately, the challenge for the future lies in bridging the gap between controlled single-chemical, single-species laboratory studies and the reality of the biodiversity impact of complex chemical mixtures interacting within dynamic, multi-stressor ecosystems.
Recorded lecture
Lorraine Maltby from the Unversity of Sheffield gives a short overview of the field of ecotoxicology.
Key Reading
Belanger SE, Rawlings JM, Ricky Stackhouse R (2018) Advances in understanding the response of fish to linear alcohols in the environment. Chemosphere 206: 539-548 https://doi.org/10.1016/j.chemosphere.2018.04.152
Hanazato T. (1998) Response of a zooplankton community to insecticide application in experimental ponds: a review and the implications of the effects of chemicals on the structure and functioning of freshwater communities. Environmental Pollution 101: 361-373 https://doi.org/10.1016/S0269-7491(98)00053-0
Lemm JU, Venohr M, Globevnik L, Stefanidis K, Panagopoulos Y, van Gils J, Posthuma L, Kristensen P, Feld CK, Mahnkopf J, Hering D, Birk S. (2021) Multiple stressors determine river ecological status at the European scale: Towards an integrated understanding of river status deterioration. Global Change Biology 27:1962–1975. https://doi.org/10.1111/gcb.15504
Maltby L, Brown AR, Faber JH, Galic N, Van den Brink PJ, Warwick O, Marshall S (2021) Assessing chemical risk within an ecosystem services framework: Implementation and added value. Science of the Total Environment 791: 148631 https://doi.org/10.1016/j.scitotenv.2021.148631
Markandya A, Taylor T, Longo A, Murty MN, Murty S, Dhavala K. (2008) Counting the cost of vulture decline—An appraisal of the human health and other benefits of vultures in India. Ecological Economics 67: 194-204. https://doi.org/10.1016/j.ecolecon.2008.04.020.
Olker JH, Elonen CM, Pilli A, Anderson A, Kinziger B, Erickson S, Skopinski M, Pomplun A, LaLone CA, Russom CL, Hoff D (2022), The ECOTOXicology Knowledgebase: A Curated Database of Ecologically Relevant Toxicity Tests to Support Environmental Research and Risk Assessment. Environmental Toxicology and Chemistry 41: 1520-1539. https://doi.org/10.1002/etc.5324
Paetzold A, Smith M, Warren PH, Maltby L. (2011) Environmental impact propagated by cross-system subsidy: chronic stream pollution controls riparian spider population. Ecology 92: 1711-1716. https://doi.org/10.1890/10-2184.1
Potts SG, Biesmeijer JC, Kremen C, Neumann P, Schweiger O, Kunin WE. (2010) Global pollinator declines: trends, impacts and drivers. Trends in Ecology & Evolution 25: 345-353 https://doi.org/10.1016/j.tree.2010.01.007
Powney GD, Carvell C, Edwards M, Morris RKA, Roy HE, Woodcock BA, Isaac NJB. (2019) Widespread losses of pollinating insects in Britain. Nature Communications 10: 1018. https://doi.org/10.1038/s41467-019-08974-9
Stravs MA, Stamm C, Ort C, Singer H. (2021) Transportable Automated HRMS Platform “MS2field” Enables Insights into Water-Quality Dynamics in Real Time. Environmental Science & Technology Letters 8: 373-380 DOI: 10.1021/acs.estlett.1c00066
Thrupp TJ, Runnalls TJ, Scholze M, Kugathas S, Kortenkamp A, Sumpter JP. (2018) The consequences of exposure to mixtures of chemicals: Something from ‘nothing’ and ‘a lot from a little’ when fish are exposed to steroid hormones. Science of The Total Environment 619–620: 1482-1492. https://doi.org/10.1016/j.scitotenv.2017.11.081.
Wang Z, Walker GW, Muir DCG, Nagatani-Yoshida K. (2020) Toward a Global Understanding of Chemical Pollution: A First Comprehensive Analysis of National and Regional Chemical Inventories. Environmental Science & Technology 54: 2575-2584 DOI: 10.1021/acs.est.9b06379
Additional reading
Ankley GT, Edwards SW. (2018) The Adverse Outcome Pathway: A Multifaceted Framework Supporting 21st Century Toxicology. Current Opinion in Toxicology 9:1-7. doi: 10.1016/j.cotox.2018.03.004.
Spromberg JA, John BM, Landis WG (1998) Metapopulation dynamics: Indirect effects and multiple distinct outcomes in ecological risk assessment. Environmental Toxicology and Chemistry 17, 1640–1649, https://doi.org/10.1002/etc.5620170828
Spurgeon D, Lahive E, Robinson A, Short S and Kille P. (2020) Species Sensitivity to Toxic Substances: Evolution, Ecology and Applications. Frontiers in Environmental Science 8: 588380. doi: 10.3389/fenvs.2020.588380