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The sub-lethal impacts of waste water effluent and its components on Gammarus pulex

Student thesis: Doctoral Thesis

  • Adrian Charles Love
The prevalence of pharmaceuticals and personal care products (PPCPs) in lotic habitats is increasing, with the main source of these contaminants being effluent from waste water treatment works (WwTW). There is still much uncertainty about the impacts of these PPCPs at environmentally relevant concentrations and their potential effects on populations. This thesis provides an evaluation into the effects of WwTW, their effluent, and the PPCP they contain on a typical and important freshwater invertebrate, Gammarus pulex, using field and laboratory observations.
A two-year investigation into G. pulex populations in sample points up-and downstream of two WwTW discharge points showed significant differences in the sizes of male and female G. pulex populations relative to the point of discharge, though the effects were not consistent between the two sites. There were more consistent changes on the frequency of intersex phenotypes and reproductive investment at and below the effluent discharge point suggesting the effluents are having a direct or indirect effect on the reproduction and development.
The impact of effluent on behaviour was measured using automated and manual means. Animals’ activity and phototaxis, as well as feeding rate and pairing tendency was measured over three weeks’ exposure to two WwTW’s final effluents at 50% and 100% concentration. There was no significant difference between activity, phototaxis and feeding responses in effluent exposed animals and controls. Pairing was significantly more rapid in animals after exposure to both effluents which may be related to reproductive effects.
A series of experiments were conducted to assess the effects of 5 PPCPs (diclofenac, fluoxetine, ibuprofen, propranolol, and triclosan), and a pharmaceutical mixture, on G. pulex. Effects were assessed in terms of activity, phototaxis, mortality, feeding rate and moulting frequency. Trials ranged from short term (1 week) exposures using toxic concentrations to chronic (3 week) exposures to environmentally relevant doses. There were significant sub-lethal effects at a range of concentrations, including hormetic responses. Significant mortalities were seen at triclosan concentrations at 0.01, 1 and 10µg L-1, and diclofenac and proporanolol concentrations of 10mg and 5mg L-1 respectively. Effects of drugs were associated with their mode of action or toxicity.
Energy reserves were measured in terms of lipid and glycogen concentration. There was no significant effect on glycogen reserves, but lipid concentrations were significantly less after exposure to 0.1 µg L1 diclofenac, 2 µg L-1 ibuprofen and 0.5 µg L-1 propranolol. Effect on reproduction was assessed through pairing frequency as well as embryo production. Significant negative effects were seen on pairing,  after exposure to environmentally relevant concentrations of fluoxetine, diclofenac and triclosan, but this was not found to impact egg production with the exception of triclosan, where a reduction in the size and development of embryos was observed at concentrations of 0.1µg L-1.
This study is the first long term investigation into G. pulex populations around WwTW. It shows the natural variability in population, sex distributions, and seasonal differences of this keystone aquatic invertebrate in two southern chalk streams receiving effluent discharges. It represents the first time the incidence and characteristics of intersex G. pulex have been studied and records a consistent increase in the frequency of this phenotype downstream of WwTWs which has not been identified before. Whether there are broader effects on intersex frequency on other invertebrates and the implications of this for the lotic ecology and water treatment processing is discussed.
Of the PPCPs tested, triclosan and diclofenac showed the most consistent toxic effects across the end points assessed, ranging from subtle behavioural effects to lethality. This is of particular concern given the widespread use and incidence of the chemicals in sewage effluent and the toxic impacts seen here at environmentally relevant doses. Both chemicals are currently undergoing reviews by European and American regulatory bodies regarding their safety, potential impacts and acceptable environmental limits. The results of this study will be of use in informing this debate.
Original languageEnglish
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Award dateSep 2017

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