What we know about the world is always changing.
In one area of science Murrang Earth Sciences works within, environmental chemistry, this is particularly the case, as scientists discover more about the behaviour and toxicity of new and old chemicals, and new methods are developed to understand how to measure chemical behaviour and toxicity in the environment.
Conferences are a really great place to catch up on these discoveries, and in October I attended the Society for Environmental Toxicology and Chemistry’s annual conference in Hobart. There were so many very good presentations and I cannot think of a single bad one. The research presented was highly relevant to industry, academia, and regulators alike, and had important ramifications regarding how we measure, assess, and control discharges of chemicals to the environment.
For this reason, this month’s blog will highlight some of my favourite talks at the conference. Unfortunately, with three sessions running concurrently over three days, it wasn’t possible for me to see all of the talks presented. Nor is there room for me to summarise all the talks I did see here. Instead, my research highlights from the conference are presented below. I strongly recommend looking at the conference programme to get insight into other talks which are not discussed below, but which have great importance for how we manage contamination in Australia.
Even the glaciers in New Zealand are contaminated with persistent organic pollutants. In a clever study, PhD student Xiaolin Wu analysed the snow and snow-melt in Brewster Lake, a glacially fed water body within New Zealand’s South Island, for a range of persistent organic pollutants including dacthal, hexachlorobenzene, endosulfan, chlorpyrifos, and triallate. She found that the concentration of some of these pollutants varied in the snow and melt water with season. This is because these are semi-volatile chemicals, which fall out of the air when it is cooler and evaporate again when it is warmer. As glaciers melt, these chemicals seem likely to be mobilised from glaciers in increasing concentrations.
The effects of some persistent organic pollutants are still being seen in wildlife, despite these being banned sometimes decades ago. Associate Professor Kimberly Hageman studied trout in New Zealand’s Clutha River and found hexachlorobenzene in almost every fish she sampled, at concentrations of up to 100 ng/g lipids. By looking at strontium isotopes in the otoliths of these fish, she could identify that different groups of fish had lived in different places, and this life history could be used to understand why some trout had higher concentrations of hexachlorobenzene than others.
Cyanobacteria produce non-protein amino acids—amino acids which are not used in the synthesis of proteins—which can be beneficial to other organisms. They may also have negative impacts on other organisms however, with the non-protein amino acids from cyanobacteria found to bioaccumulate and cause motor neuron disease in humans and bats exposed to them. Kate Samardzic’s research on this subject has found that non-protein amino acids are also used by cyanobacteria to attack (through allelopathy) other plants and, if crops are irrigated using water contaminated with cyanobacteria, could cause substantial losses.
Neuroendocrine disruption is a term coined in 2011, and is the study of how the brain’s control of hormones is disrupted. In two troubling talks, the neuroendocrine effects of the chemicals fluoxetine (the active ingredient in Prozac) and diclofenac (the active ingredient in Voltaren) were discussed in regards to the effects of these chemicals on the behaviour of exposed organisms. Professor Vance Trudeau showed how reproduction and behaviour of fish are interrupted by exposure to fluoxetine. PhD student Jack Martin showed that at environmentally realistic concentrations, diclofenac substantially alters the antipredator behaviour of Eastern mosquitofish, and that male and female fish behaved differently after exposure to this chemical. Perhaps most troubling of all was Professor Trudeau’s research which showed that Bisphenol A (BPA), a chemical associated with plastics, has been found to have intergenerational effects in rats—i.e. the exposure of a parent generation of rats to BPA causes neurological impacts to the next generation who is not exposed to this chemical.
People have known about the antimicrobial properties of silver for thousands of years, and silver is still used today in hospitals to treat burns. Recently, there has been a huge increase in the number of silver-containing products, such as socks, washing powders, and face creams, marketed for these antimicrobial properties (among others). Associate Professor Erica Donner presented research regarding the effects of this increased silver load arriving in sewage treatment plants and how bacteria now have selection pressure to evolve resistance to it. This microbial evolution of silver resistance presents a substantial threat to human health, as we still rely on silver to prevent burns from becoming infected, and the reuse of biosolids presents a realistic pathway for this antimicrobial resistance to be introduced into the environment.
There is no such thing as a clean piece of plastic in the environment—many pollutants are attracted to them. Dr Bradley Clarke presented research which showed that polybrominated diphenyl ethers (PBDEs) adhere to microplastics. When these plastics are ingested by fish they facilitate accumulation of PBDE in the fish. Research by PhD student Amanda Dawson showed that microplastics now occur in even remote locations such as Antarctica, where krill chomp them up into even smaller pieces (“nanoplastics”) which are also ingested. Viewed together, the research presented by these two presenters indicates microplastics now represent a new exposure pathway for chemicals to organisms in the environment.
The toxicity and availability of metals in the environment is well known to be affected by pH and reduction-oxidation potential. In a series of wonderful talks, the effects of other factors were also presented. Dr Aleicia Holland presented research showing how different types and concentrations of dissolved organic carbon in water affected metal toxicity. She found that allochthonous dissolved organic carbon (terrestrially-derived, highly aromatic carbon molecules with high molecular weight) at pH 7 decreased nickel toxicity. Dr William Bennett presented how seawater inundation effects metals' contaminated sediments. Metals which sorb to organic matter via oxygen containing ligands like carboxyl groups were mobilised. Those with sulfur containing ligands such as thiol groups were more immobile. Hard-soft acid-base theory was used as a basis to understand this variation in metal mobility.