Classic and temporal mixture synergism in terrestrial ecosystems: Prevalence, mechanisms and impacts

生活在地上和地下的无脊椎动物物种是陆地食物网的核心，也是碳循环、土壤肥力和害虫控制的关键贡献者。这些重要物种中有许多极易受到化学污染的影响。这些物种经常接触的化学物质的范围正变得越来越复杂。例如，与15年前相比，农民在耕地作物上使用的农药种类增加了50%，越来越多的化学物质从我们的家庭和工业废物中进入生态系统。化学品生产商、使用者和监管机构面临的一个挑战是找到方法，使化学品使用的好处最大化，同时将任何负面影响降到最低。支持更好地对化学品进行“生态风险评估”的科学研究是应对这一挑战的核心。我们今天使用的许多化学物质来自新的、研究较少的化合物类别，它们可以以不同的方式影响不同物种的生物过程。我们目前对这些化学物质缺乏了解，因此很难评估它们的生态影响。当我们意识到污染物几乎总是以混合物的形式出现时，事情就变得更加复杂了。如果我们想要正确地解决和避免不必要的化学影响，我们需要更好地理解和考虑化学混合物。预测污染物混合物对无脊椎动物和生态系统可能产生的影响最常用的方法是假设化学物质之间不相互作用，因此它们的毒性可以加在一起。这种相对简单的“加法”方法在大多数情况下都是有效的。然而，对于相当大比例的混合物（根据包括的化学类别，高达20%），观察到的效果比基于添加的预期更差。当这种“协同作用”发生时，基于可加性的混合物环境保护政策将低估实际效果（见图1，支持案例）。显然这是一个问题。为了解决这个问题，我们需要确定相互作用的化学混合物，并预测最有可能产生协同作用的原因。反过来，这要求我们了解混合物中不同化学物质的毒性机制如何与暴露物种的不同生化、生理和生态特性相互作用，从而产生协同作用。这个项目的主要目的是获取和应用这些知识。我们自己的研究已经确定了一些化学混合物更有可能表现出协同作用，对接触无脊椎动物的毒性更高。例如，在下列情况下：(a)一种化学品影响另一种化学品解毒或活化的方式；或(b)一种化学品增加对另一种化学品的生物吸收；或(c)先前接触一种化学品会改变另一种化学品的生物毒性，这取决于接触的时间。然而，我们还远远不能理解所有的情况。因此，本项目旨在改变我们在常见陆地污染情景（农用化学品使用、废物投入）中确定、量化和预测协同潜力的能力。我们将与伙伴机构合作，确定与陆地生态系统有关的可能具有协同作用的化学污染物混合物，并进行实验，测试它们对一系列无脊椎动物物种的影响。当我们在一个物种中观察到协同作用时，将对其他物种进行测试，以发现这是否是一种普遍效应。生物化学和遗传方法将用于确定毒性机制和与协同作用相关的物种特征，整合这些信息来开发模型和新的预测工具。为了确保我们在实验室看到的效果与现场相关，我们将在室外系统中进行研究，以测试自然群落中协同作用的存在。最后，我们将利用我们的发现制作一份POSTnote“白皮书”，详细说明未来的风险评估政策如何明确考虑协同作用以支持环境保护。

Invertebrate species living above and below ground are central to terrestrial food webs and key contributors to carbon cycling, soil fertility and pest control. Many of these important species are highly vulnerable to chemical pollution. The range of chemicals these species are regularly exposed to is becoming increasingly complex. For example, farmers now use 50% more types of pesticide on arable crops than they did 15 years ago and an ever-increasing diversity of chemicals enter ecosystems from our domestic and industrial wastes. A challenge for chemical producers, users and regulators is to find ways to maximise the benefits of chemical use, while minimising any negative effects. Scientific research to support better 'ecological risk assessment' of chemicals is central to meeting this challenge. Many of the chemicals we use today come from new, less well studied, compound classes that can affect biological processes, in diverse ways, in different species. Our current lack of knowledge about these chemicals makes their ecological effects difficult to assess. Things become more complicated when we realise that pollutants almost always occur as mixtures. If we want to properly to address and avoid unwanted chemical impacts, we need to better understand and take account of chemical mixtures. The most commonly used way to predict the likely effects of pollutant mixtures on invertebrates and ecosystems assumes that chemicals do not interact with each other and that, therefore, their toxicities can be added together. This relatively simple 'additive' approach has been shown to work most of the time. However, for a substantial proportion of mixtures (up to 20% depending on chemical classes included), the observed effects are worse than expected based on addition. Where such 'synergy' occurs, environmental protection policies for mixtures based on additivity will underestimate actual effects (see Fig. 1, Case for Support). Clearly this is a problem. To address it, we need to identify interactive chemical mixtures and predict the most likely causes of synergy. In turn, this requires us to understand how the mechanisms of toxicity of different chemicals in a mixture interplay with the different biochemical, physiological and ecological traits of exposed species to cause synergy. The main aim of this project is to gain and apply this knowledge. Our own research has identified some chemical mixtures that are more likely to show synergy, with higher levels of toxicity to exposed invertebrates. For example, where: (a) a chemical affects the way that another is detoxified or activated; or (b) a chemical increases the biological uptake of another chemical; or (c) prior exposure to a chemical changes the biological toxicity of another chemical, depending on the timing of exposure. However, we are very far from understanding all cases. Thus, this project aims to transform our ability to identify, quantify and predict the potential for synergy in common terrestrial pollution scenarios (agrochemical use, waste inputs). Working with partner agencies, we will identify potentially synergistic chemical pollutant mixtures, relevant to terrestrial ecosystems, and conduct experiments to test their effects on a range of invertebrate species. When we observe synergy in one species, other species will be tested to discover if this is a general effect. Biochemical and genetic methods will be used to identify mechanisms of toxicity and species traits associated with synergism, integrating this information to develop models and new predictive tools. To ensure the effects we see in the laboratory are relevant to the field, we will conduct studies in outdoor systems to test for the presence of synergism in natural communities. Ultimately, we will use our findings to produce a POSTnote 'White paper' detailing how future risk assessment policies can explicitly consider synergism to support environmental protection.