Unravelling the physiological drivers of species accumulation and sensitivity for metals

Metals are one of the most common pollutants of our soils. However, whether these potential poisons are taken up by an organism and what the subsequent toxic effects are is only known for a small number of species - usually those easily maintained in the laboratory or very common and widespread in the field. The limited scope of our current understanding of metal "accumulation" and the linked "toxicity" in different species makes it difficult for us to predict and monitor the negative effects that metal pollution has on ecosystems - whether directly due to toxicity or as a result of predators eating contaminated prey.

We know from past work that even among the limited species tested, metal accumulation and toxicity can vary greatly. Further, we already know some of the main ways that metals can cause toxicity and also some of the systems active in cells by which such effects can be prevented through "detoxification". For metals this process is often associated with changing the form of the metal to an inert inorganic compound, locking it away into intracellular compartments or binding it to different proteins and/or peptides. What we currently do not know, however, is how these mechanisms and systems contrast between species and how this inter-species variations, in turn, lead to differences in the extent of accumulation and linked toxic effect.

In this project, we want to develop a "framework" that unifies understanding of how metals are taken up by different soil animals, distributed between tissues, change their chemical associations and cause damage to cells, organs and the organism as a whole, resulting ultimately in toxicity for a species. Our framework is based on developing understanding in three areas.

i) Measuring the rates at which a metal enters into, and is distribute, between the tissue of soil animals.
We will quantify this by analysing metal levels in major tissues, using radio-labelled compounds to assess uptake and loss and generating tissue maps to determine where and how much metal is accumulating in the body. For larger invertebrates we will dissect the tissue but for the smaller organisms we will use state-of-the-art laser assisted mapping technologies.

ii) Assessing the way that metals change their chemical associations on up taken into an organism, either through chemical reactions, compartmentalisation or by binding.
We will measure these processes by analysing the chemical form of the metals within different pools in separated tissue samples and by using X-ray methods that determine the co-localisation of metals with other elements and known metal binding molecules.

iii) Evaluating the resultant damage to cells and tissues from exposure to the different metal forms.
This will be measured by assessing biochemical responses associated with damage and linking these to the pathways that regulate metal accumulation and the chemical form present within the organism. We will determine how the damage caused translates through various levels of biological organisation to result in toxicity at the level of the whole organism.

Studying these three aspects for four metals (manganese, lead, copper and cadmium) that have different dominant chemistries and essentialities in eight common and ecologically important soil invertebrate species, will allow us to develop a new model that describes the processes that lead to metal accumulation and toxicity. This approach will greatly improve on the current approaches used in ecosystem focused toxicology, which have so far focused on external metal chemistry in the soil and how this impacts on exposure. Further, developing this organism-focused model, will allow us to extend our studies to other species beyond those studied here to more easily predict how much of a given metal each may accumulate and just what toxic impacts will result. This capacity will significantly advance on the current approaches used in comparative ecotoxicology.