Over the past decade, there has been increasing scientific interest in the occurrence, fate and effects of pharmaceuticals in the environment. To date, the majority of this research has focussed on the aquatic environment whilst the terrestrial environment has remained relatively unexplored. Research carried out in the terrestrial environment has primarily focussed on the fate of pharmaceuticals in soils as well as the uptake of pharmaceuticals into plants. Less information is available on the uptake of pharmaceuticals into other soil dwelling species.
The studies presented in the thesis were therefore performed to investigate the uptake of pharmaceuticals into earthworm species (Eisenia fetida and Lumbricus terrestris) and plant species (radish and ryegrass). Experiments were designed to explore the effect of pharmaceutical physico-chemical properties, soil parameters and species traits on the uptake of pharmaceuticals from soils into terrestrial species. Understanding the factors and processes involved in the uptake of these compounds from soils, is vital to adequately assess the risks of pharmaceuticals in the environment.
Initial experimental studies evaluated the uptake of four pharmaceuticals, namely carbamazepine, diclofenac, fluoxetine and orlistat into the earthworm, Eisenia fetida. Pore water based bioconcentration factors (BCFs) increased in the order of carbamazepine < diclofenac < fluoxetine and orlistat.
As well as experimental research, a desk based investigation was perfomed to assess the applicability of a minimised design approach to estimate bioconcentration factors (BCFs) in terrestrial and aquatic species. A significant regression between BCFminimised and BCFtraditional was found and this approach was therefore adopted to calculate earthworm BCFs in the soil parameters and species traits studies described below.
The uptake of the four study pharmaceuticals by E. fetida was therefore further evaluated in different soil types. The uptake and accumulation of pharmaceuticals into E. fetida changed depending on soil type. Orlistat exhibited the highest pore water based bioconcentration factors (BCFs) and displayed the largest differences in uptake between soil types as BCFs ranged between 30.51 – 115.92. For carbamazepine, diclofenac and fluoxetine BCFs ranged between 1.05 – 1.61, 7.02 – 69.57 and 16.78 – 20.42 respectively.
Supplementary studies compared the uptake of the study pharmaceuticals in two earthworms (Lumbricus terrestris and E. fetida). All four pharmaceuticals were taken up by both L. terrestris and E. fetida tissue after 21 d exposure to spiked soil. Pore water based bioconcentration factors (BCFs) ranged between 6.69 and 83.79 for L. terrestris and 1.14 and 63.03 for E. fetida.
The effect of species type on the uptake of pharmaceuticals (carbamazepine, diclofenac, fluoxetine, propranolol, sulfamethazine) and a personal care product (triclosan) was also investigated in plant species (radish, Raphanus sativus and ryegrass, Lolium perenne). Five of the six chemicals were taken up into plant tissue, carbamazepine to the greatest extent in both the radish (52 µg/g) and ryegrass (33 µg/g) whereas sulfamethazine uptake was below the limit of quantitation (LOQ).
The results demonstrate the ability of plant species and earthworms to accumulate pharmaceuticals from soils with uptake apparently specific to both species, chemical and soil type. However the influence of these individual parameters does not affect BCFs to a significant amount. The research also highlights that a combination of factors and processes appear to be driving the uptake into soil dwelling species as further analysis was unable to find a single parameter to adequately explain pharmaceutical uptake into terrestrial species. For example, for plant uptake, results could only be partly explained by the hydrophobicity and extent of ionisation of each chemical in the soil.
Even though these chemicals are taken up by earthworms and plants, further analysis showed that the risk to predatory birds is minimal based on the current environmental scenarios as thousands of worms would have to be consumed by a bird to receive a single dose. Similarly, the potential risk to humans consuming crops contaminated with pharmaceutical residues is also minimal. However with increasing loadings of pharmaceuticals to soils this may result in potential problems for human health and predatory birds in the future.
