Paul K. Sibley

TOXICITY OF HUMAN PHARMACEUTICALS AND PERSONAL CARE PRODUCTS TO BENTHIC INVERTEBRATES

Despite concerns about potential risks associated with the presence of pharmaceuticals and personal care products (PPCPs) in the environment, few toxicological data address the effects of these compounds. In aquatic systems, which often represent the final repository for PPCPs, increasing toxicological information regarding aquatic biota is improving our capacity to assess potential risks. However, responses of key biota, such as benthic invertebrates, have not been investigated as widely. In the present study, we examined the toxicity of four PPCPs -- the lipid regulator atorvastatin (ATO), the antiepileptic drug carbamazepine (CBZ), the synthetic hormone 17alpha-ethinylestradiol (EE(2)), and the antimicrobial triclosan (TCS) -- to the midge Chironomus tentans and the freshwater amphipod Hyalella azteca in 10-d waterborne exposures. The toxicity of the four compounds varied between 0.20 and 47.3 mg/L (median lethal concentration), with a relative toxicity ranking of TCS > EE(2) > ATO > CBZ. Hyalella azteca was more sensitive than C. tentans to these compounds. The toxicity data were used in a hazard quotient approach to evaluate the risk posed by the four PPCPs to benthic invertebrates and other aquatic organisms. For each compound, a hazard quotient was calculated by dividing the lowest toxicity value by the highest exposure value found in the literature, to which an uncertainty factor was applied. With hazard quotients of 3.55 to 11.5, we conclude that potential risks exist toward benthic invertebrates for the toxicity of TCS and CBZ and that further investigations of these compounds are required to characterize more completely the risks to benthic organisms. In contrast, our data also indicate that considering the low concentrations currently detected in the environment, ATO and EE(2) pose negligible risks to benthic invertebrates.

Effects of Ten Antibiotics on Seed Germination and Root Elongation in Three Plant Species

We applied a screening-level phytotoxicity assay to evaluate the effects of 10 antibiotics (at concentrations ranging from 1 to 10,000xa0μg/L) on germination and early plant growth using three plant species: lettuce (Lactuca sativa), alfalfa (Medicago sativa), and carrot (Daucus carota). The range of phytotoxicity of the antibiotics was large, with EC25s ranging from 3.9xa0μg/L to >10,000xa0μg/L. Chlortetracycline, levofloxacin, and sulfamethoxazole were the most phytotoxic antibiotics. D. carota was the most sensitive plant species, often by an order of magnitude or more, followed by L. sativa and then M. sativa. Plant germination was insensitive to the antibiotics, with no significant decreases up to the highest treatment concentration of 10,000xa0μg/L. Compared with shoot and total length measurements, root elongation was consistently the most sensitive end point. Overall, there were few instances where measured soil concentrations, if available in the publicly accessible literature, would be expected to exceed the effect concentrations of the antibiotics evaluated in this study. The use of screening assays as part of a tiered approach for evaluating environmental impacts of antibiotics can provide insight into relative species sensitivity and serve as a basis by which to screen the potential for toxic effects of novel compounds to plants.

Transgenerational shifts in reproduction hormesis in green peach aphid exposed to low concentrations of imidacloprid.

Hormesis is a biphasic phenomenon that in toxicology is characterized by low-dose stimulation and high-dose inhibition. It has been observed in a wide range of organisms in response to many chemical stressors, including insects exposed to pesticides, with potential repercussions for agriculture and pest management. To address questions related to the nature of the dose-response and potential consequences on biological fitness, we examined transgenerational hormesis in the green peach aphid, Myzus persicae, when exposed to sublethal concentrations of the insecticide imidacloprid. A hormetic response in the form of increased reproduction was consistently observed and a model previously developed to test for hormesis adequately fit some of our data. However, the nature of the dose-response differed within and across generations depending upon the duration and mode of exposure. Decreased reproduction in intermediate generations confirmed that fitness tradeoffs were a consequence of the hormetic response. However, recovery to levels of reproduction equal to that of controls in subsequent generations and significantly greater total reproduction after four generations suggested that biological fitness was increased by exposure to low concentrations of the insecticide, even when insects were continuously exposed to the stressor. This was especially evident in a greenhouse experiment where the instantaneous rate of population increase almost doubled and total aphid production more than quadrupled when aphids were exposed to potato plants systemically treated with low amounts of imidacloprid. Our results show that although fitness tradeoffs do occur with hormetic responses, this does not necessarily compromise overall biological fitness.

Measuring bioaccumulation of contaminants from field-collected sediment in freshwater organisms: a critical review of laboratory methods

To be effective, decision-making frameworks require data from robust and reliable test methods. Using standard methods allows for more effective comparison between studies and application of data, and it reduces unnecessary duplication of efforts. Laboratory methods to assess the toxicity of sediment have been standardized and extensively used; however, procedures for measuring the bioaccumulation of contaminants from sediment into aquatic organisms need further standardization. Bioaccumulation methods using freshwater invertebrates and fish exposed to field-contaminated sediment were reviewed to identify important similarities and differences in method protocols, test conditions that need to be controlled, and data gaps. Although guidance documents are available, great variation still exists in exposure techniques used in tests, which may potentially affect the estimation of bioaccumulation. The techniques most consistent across studies include the use of Lumbriculus variegatus as a test species, test temperatures between 20 and 25°C, and a 28-d exposure with no addition of food, followed by purging of organisms. Issues that were inconsistent between studies or remained unspecified, which should be addressed, include the bioaccumulation potential of other test species, loading density of organisms, and sediment-to-water ratio. In addition to proper evaluation of the various exposure techniques and conditions, a need exists for more consistent inclusion of quality control procedures during testing.

Structural responses of Daucus carota root-organ cultures and the arbuscular mycorrhizal fungus, Glomus intraradices, to 12 pharmaceuticals

Pharmaceuticals and personal care products may enter the terrestrial environment through the amendment of agricultural soils with manure or biosolids with potential impacts on beneficial soil microbe populations. The beneficial symbiotic relationship between most plant species and arbuscular mycorrhizal fungi is a primary determinant of plant health and soil fertility. As such, there is increasing recognition of the need to study the impacts of anthropogenic stressors on plant-microbe interactions in soil ecotoxicology studies and risk assessment. A case study exploring the use of root-organ cultures to evaluate the effects of 12 common veterinary and human-use pharmaceuticals on the arbuscular mycorrhizal fungus, Glomus intraradices grown on Daucus carota root-organ cultures is presented. The bioassays were conducted over a 28-day exposure period at concentrations up to 1000microgl(-1). Root length and the fungal endpoints of hyphal growth and spore production were evaluated weekly during the study. Sulfamethoxazole and atorvastatin were the most phytotoxic compounds with EC50 values of 45microgl(-1) and 65microgl(-1), respectively. Three compounds exhibited selective mycotoxicity, whereby the fungal symbiont was adversely affected at concentrations significantly less than that calculated for root length. The EC50 for G. intraradices hyphal length was 45microgl(-1) for doxycycline, while carbamazepine and 17-alpha-ethynyl estradiol targeted spore production with EC50 values of 113 and 116microgl(-1), respectively. The assay results indicate that the root lengths responded quickly to the presence of phytotoxic pharmaceuticals in the culture medium. Hyphal length is a sensitive endpoint after 21 days exposure, while spore production requires 28 days exposure before significant differences could be detected. Root-organ cultures provide an effective means to evaluate chemical stressors on arbuscular mycorrhizal fungi and can be used to screen for root-based phytotoxicity.

Matrix effects on mass spectrometric determinations of four pharmaceuticals and personal care products in water, sediments, and biota

Simple analytical methods were developed for the extraction and determination of four pharmaceuticals and per- sonal care products (PPCPs) from water, sediments, and biota. PPCPs were determined using tandem LC-MS in electro- spray ionization mode, and interactions with matrix co-eluents were investigated. Extractions of water samples were performed using solid-phase extraction (SPE), sediments were extracted by pressurized liquid extraction (PLE), and biota was extracted by liquid extraction. The selected analytical methods yielded recoveries ‡ 61% in all matrixes. Matrix inter- actions were investigated throughout the linear range of quantification of each compound, revealing that dissolved salts had relatively minor effects on ionization (between 14% suppression to 12% enhancement), but that sediment and biota ex- tracts caused significant matrix effects (ranging from 56% suppression to 25% enhancement). The direction and magnitude of matrix interactions reflected the physico-chemical properties of each analyte, particularly their pKa. Among the com- pounds analyzed in electrospray positive mode, carbamazepine was insensitive to matrix interactions, because it is a strong proton acceptor (pKa = 14.0). In contrast, atorvastatin (pKa = 4.5), a weaker proton acceptor, was particularly sensitive to matrix effects. For those compounds analyzed in negative-ion mode, sample alkalinity was found to be important. With a pKa of 10.4, 17a-ethinylestradiol generally exhibited matrix enhancement with increased sample alkalinity. However, the presence of acidic co-eluents contributed to matrix suppression. Lastly, TCS was particularly sensitive to matrix suppres- sion, as its circumneutral pKa (7.9) caused even slight changes in sample pH to considerably impact ionization. We con- clude that while different matrixes have clear impacts on ionization of these PPCPs, matrix effects can be quantified and overcome.

The importance of catchment slope to soil water N and C concentrations in riparian zones: implications for riparian buffer width

Buffer zones are an important component of forest-management strategies and are thought to reduce the impact of nutrients released after harvesting on water quality. Conceptually, steep slopes have shorter water residence times than shallow slopes, have a reduced capacity to moderate water quality, and therefore, require wider buffers. Carbon and N concentrations in riparian zone shallow soil water at 30 cm depth and lake water were measured on shallow and steep slopes at the Esker Lakes Research Area in northeastern Ontario to determine if nutrient concentrations were correlated to catchment terrain attributes. Field measured slope, slope class obtained from a triangular irregular network model, and up- slope contributing area and topographic index calculated from a digital elevation model were calculated for each sampling location. Modeled terrain properties, including those currently used during forest-management planning, were not signifi- cantly correlated with soil water N and C concentrations, whereas only dissolved organic carbon levels were significantly greater on field measured steep slopes. Forest species composition and soil N levels were positively correlated with soil water N concentrations. These results from the undisturbed boreal ecosystem highlight the potential limitation of using only catchment slope as a tool for prescribing riparian buffers during harvesting when considering terrestrial nutrient export. Resume´ : Les zones tampons constituent une composante importante des strategies damenagement forestier et pourraient reduire limpact de la liberation des nutriments sur la qualitede leau apres la coupe. De facon conceptuelle, les pentes fortes sont caracterisees par des temps de residence de leau plus courts que ceux des pentes douces et une moins grande capacitea attenuer les effets sur la qualitede leau et, par consequent, exigent des zones tampons plus larges. La concen- tration en C et N de leau situeeaune profondeur de 30 cm dans le sol de zones riveraines et de leau de lac a eteme- suree le long de pentes fortes et douces de laire de recherche des lacs Esker dans le nord-est de lOntario dans le but de determiner si la concentration en nutriments etait correlee aux attributs de terrain des bassins versants. Pour chaque point dechantillonnage, nous avons mesurela pente sur le terrain, obtenu la classe de pente a laide dun modele de terrain basesur un reseau trianguleirregulier et calculelaire contributoire de haut de pente ainsi quun indice topographique avec un modele altimetrique numerique. Les proprietes du terrain modelisees, incluant celles couramment utilisees au cours de la planification de lamenagement forestier, netaient pas significativement correlees aux concentrations de N et de C dans leau du sol alors que seuls les niveaux de carbone organique dissous etaient significativement plus eleves sur les pentes fortes mesurees sur le terrain. La composition en especes forestieres et les niveaux de N dans le sol etaient posi- tivement correlesala concentration de N de leau du sol. Ces resultats issus dun ecosysteme boreal non perturbemettent en evidence les limites potentiellement associees a lutilisation seule de la pente des bassins versants comme outil pour de ´- terminer les zones riveraines tampons lors de la coupe lorsque lexportation des nutriments terrestres est consideree. (Traduit par la Redaction)

The Effect of Organism Density on Bioaccumulation of Contaminants from Sediment in Three Aquatic Test Species: A Case for Standardizing to Sediment Organic Carbon

Laboratory methods for measuring bioaccumulation of organic contaminants from sediment into aquatic organisms continue to improve, but some aspects are still in need of standardization. From a review of published methods, we noted that the loading density of organisms was determined inconsistently and was primarily based on either sediment volume or total organic carbon (TOC). The rationale mainly expressed for standardizing to TOC was to minimize the depletion of sediment contaminants. However, even when density was standardized to TOC, the relative amount of TOC provided (i.e., ratio of TOC to organism dry weight [dw]) was highly variable. In this study, we examined the effect of organism density (standardized to sediment TOC or volume) on bioaccumulation in three freshwater organisms. The oligochaete Lumbriculus variegatus, mayfly nymph Hexagenia spp., and fathead minnow Pimephales promelas were exposed for 28xa0days to two field-contaminated sediments that varied in concentration of PCBs and TOC. Densities tested were 50:1 and 27:1 ratios of TOC to organism dw and 140xa0ml sediment/g wet weight (ww) biomass, yielding low to high organism densities. Bioaccumulation in Hexagenia spp. was significantly higher at the lowest organism density compared with the highest organism density when exposed to site 2 sediment (1.1% TOC) but only with tissue concentrations expressed on a ww basis. Otherwise, there was no significant effect of density on bioaccumulation in organisms exposed to sediments from site 1 (12% TOC) or site 2. Survival of Hexagenia spp. was adversely affected at the highest organism density when the relative amount of TOC was low. The results of this study support the recommendation of standardizing organism density relative to a particular amount of TOC for invertebrate species. A 27:1 ratio of TOC:organism dw was selected as a standard organism density for a new bioaccumulation method because survival, growth, and bioaccumulation were not impacted relative to a 50:1 ratio, and less sediment was required. This density is recommended as an appropriate ratio for sediment bioaccumulation assessments in general.

The influence of riparian vegetation on leaf litter inputs to Boreal Shield streams: implications for partial-harvest logging in riparian reserves

Litter inputs to headwater streams were measured to characterize and describe input patterns to the streams and to quantify the relationships between leaf litter inputs and surrounding riparian characteristics in Boreal Shield forests. Our goal was to provide information on litter inputs to streams in the Boreal Shield to determine if partial-harvest logging of commercial trees within riparian reserves has the potential to cause significant changes to litter inputs. Total leaf litter comprised 87% deciduous leaves and 13% conifer needles during the June to October periods. Commercial deciduous tree species accounted for approximately 50% of total deciduous leaf litter inputs. Distance-weighted deciduous basal area was the best predictor of overstorey deciduous litter (r 2 = 0.597, P = <0.001), indicating that the size, abundance, and proxim- ity of deciduous trees to streams are important to deciduous litter inputs. Leaf litter inputs to Boreal Shield streams are strongly influenced by surrounding riparian vegetation and can be effectively predicted by stem basal area. A linear regres- sion model based on commercial deciduous tree basal area is presented that can be useful to determine the number of trees to retain within a riparian area to maintain leaf litter inputs at or near preharvest levels. Resume´ : Les apports de litiere dans les cours deau de tete ont etemesures pour caracteriser et decrire le profil de ces apports dans les cours deau et quantifier les relations entre les apports de litiere de feuilles et les caracteristiques river- aines environnantes dans les forets du bouclier boreal. Notre but etait de fournir de linformation au sujet des apports de li- tiere dans les cours deau du bouclier boreal pour determiner si une coupe partielle des tiges marchandes dans les bandes riveraines peut entraoˆner des changements significatifs dans les apports de litiere. La litiere de feuilles totale etait compo- see de 87 % de feuilles dessences feuillues et de 13 % daiguilles de coniferes durant la periode allant de juin aoctobre. Les especes feuillues marchandes representaient approximativement 50 % de toute la litiere de feuilles provenant des- sences feuillues. La surface terriere des essences feuillues ponderee par la distance etait le meilleur predicteur de la litiere des essences feuillues de letage dominant (r 2 = 0,597, P = <0,001), ce qui signifie que la taille et labondance des arbres feuillus et leur proximitedes cours deau sont des facteurs importants dans les apports de litiere dessences feuillues. Les apports de litiere de feuilles dans les cours deau du bouclier boreal sont fortement influences par la vegetation riveraine environnante et on peut reussir ales predire au moyen de la surface terriere des arbres. Un modele de regression lineaire basesur la surface terriere des essences feuillues marchandes est presente ´. Ce modele peut etre utile pour determiner com- bien darbres il faut conserver dans une zone riveraine pour maintenir les apports de litiere de feuilles au meme niveau ou presque quavant la coupe. (Traduit par la Redaction)

Over-winter decomposition and associated macroinvertebrate communities of three deciduous leaf species in forest streams on the Canadian Boreal Shield

The decomposition of deciduous leaf material provides a critical source of energy to aquatic food webs. Changes to riparian forests through harvesting practices may alter the species composition of deciduous leaf material entering streams. We compared over-winter decomposition of three different riparian leaf species (speckled alder (Alnus incana ssp. rugosa (Du Roi) J. Clausen), white birch (Betula papyrifera Marsh.), and trembling aspen (Populus tremuloides Michx.)) to determine their importance as a food resource for macroinvertebrate communities within Boreal Shield streams in northeastern Ontario, Canada. Leaf pack decomposition of the three leaf species formed a processing continuum throughout winter, where alder and birch leaf packs decomposed at a medium rate (kxa0=xa00.0065/day and 0.0053/day, respectively) and aspen leaf packs decomposed more slowly (kxa0=xa00.0035/day). Macroinvertebrate community colonization on leaf packs changed through time regardless of leaf species. Alder leaf packs supported higher abundances of macroinvertebrates in the fall while aspen leaf packs supported greater shredder abundances in the following spring. The study shows that leaf diversity may be important for providing a sustained food resource for aquatic macroinvertebrates throughout the relatively long over-winter period in Canadian Boreal Shield streams. Riparian forest management strategies should ensure that deciduous plant species richness is sustained in riparian areas.