| Pharmaceuticals are biologically active, ubiquitous, low-level contaminants which are continuously introduced into the environment at volumes comparable to pesticides. Typically detected in the ng/L to mug/L range, the effects of these contaminants in the aquatic environment are largely uncharacterized. In order to address this data gap, over 30 pharmaceuticals were screened through laboratory assays with Lemna gibba, 12 in aquatic microcosms with L. gibba, Myriophyllum sibiricum and/or Myriophyllum spicatum, and 2 at the molecular/biochemical level in L. gibba. Among the pharmaceuticals initially screened, only fluoroquinolone, sulfonamide, and tetracycline antibiotics proved to be phytotoxic between 10-1000 mug/L, however, no significant risks were found using conservative assumptions. Similarly, a microcosm assessment with an eight pharmaceutical mixture indicated no significant risks for either L. gibba or M. sibiricum, though fluoroquinolone (levofloxacin) and sulfonamide (sulfamethoxazole) antibiotics, as well as a blood lipid regulator (atorvastatin) were identified as phytotoxic components. Tylosin, a macrolide antibiotic heavily used as a prophylactic in Canadian agriculture, was found to cause no statistically significant inhibition in any endpoint measured in L. gibba or M. spicatum evaluated singly in aquatic microcosms. Although a mixture of tetracyclines was found to pose little risk to the floating macrophyte L. gibba, the submerged macrophyte M. sibiricum showed significant inhibition and potential risks, largely because of the reduction in light penetrating the water column by as much as 99.8% at a depth of 70 cm caused by parent compounds and/or metabolites. A probabilistic ecological hazard assessment designed to address the unique data availability of pharmaceuticals revealed low probability for risk to aquatic macrophytes in all cases, with the exception of tetracyclines. Statin class blood lipid regulators were found to significantly reduce metabolite levels (sterols) downstream of the target enzyme (3-hydroxy-3methylglytaryl coenzyme-A reductase) in the mevalonic acid pathway by as much as 90%. However, no significant hazards were identified, though these pathway-specific endpoints were on average 3 times more sensitive than gross morphological endpoints. Therefore, from the subset of pharmaceuticals tested, these compounds appear to pose little risk to aquatic higher plants, evaluated in the laboratory, microcosms or using pathway-specific endpoints. |
