Gladys L. Stephenson

The impact of two applications of atrazine on the plankton communities of in situ enclosures

Abstract Atrazine (2-choro-4-ethylamino-6-isopropylamino- s -triazine) was applied to aquatic enclosures in Lake St. George, Canada (43°57′25″ N, 79°26′30″ W) on June 1 1983 with a second application 35 days later. A nominal concentration of 0.1 mg/l was used during each application. Compared to single atrazine applications, this multiple treatment was characterized by a more gradual killing of the phytoplankton, a longer period of recovery for the green algal community, and a distinct shift in the taxonomic composition of the affected communities. Thirteen days after the first application significant declines in the populations of Elakatothrix gelatinosa, Sphaerocystis schroeteri, Tetraedron minimum, Oocystis lacustris , and Gymnodinium spp. were observed. Low numbers persisted after the second application and remained lower for 114 days. Populations of Rhodomonas minuta increased significantly on day 13, whereas those of Cryptomonas erosa were not influenced by the herbicide. On average there was a reduction from 22 to 16 prominent phytoplankton taxa after atrazine exposure. The similarity between phytoplankton communities in control and atrazine-exposed enclosures, as measured by the Morisita coefficient of association, was distinctly altered after the second atrazine application. This dissimilarity persisted for 77 days. In the spring of 1984, 323 days after the first atrazine application, the control and atrazine exposed enclosures had returned to similar phytoplankton assemblages. The rotifer community was not significantly affected. Two crustaceans, Bosmina longirostris , and Diaptomus oregonensis had significant short term reductions in numbers after the second application. These reductions were not observed after the first atrazine applications and it is suggested that their decline is a secondary effect caused by changes in other populations within the community.

Acute toxicity of pure pentachlorophenol and a technical formulation to three species of Daphnia

The acute toxicity of a technical formulation of pentachlorophenol (PCP) and pure pentachlorophenol to three age classes ofDaphnia magna, and adultD. pulex andD. galeata mendotae was determined by static toxicity tests. The influence of a number of factors on toxicity of PCP was also examined. The 48-hr LC50 estimates for adult daphnids of the three species exposed to pure PCP were 1.78, 4.59 and 0.51 mg/L, respectively, while those for the technical formulation were 2.57, 3.66 and 0.33 mg/L, respectively. There was little difference in toxicity between the technical and pure PCP; however, toxicity of both forms of PCP was influenced by duration of exposure, age (and/or size) and species of test organism and pH of the test solution.Pentachlorophenol caused a toxic response over a very narrow range of concentrations, with the greatest response occurring immediately between 0 and 24 hr. Pure PCP was equally toxic to all age classes ofD. magna but susceptibility to technical PCP decreased with maturation.D. g. mendotae was ten times more sensitive thanD. pulex to PCP. Pure PCP was significantly more toxic toD. magna at pH 5.5 than 7.0 with mean 48-hr LC50 values of 0.082 and 1.78 mg PCP/L, respectively.At 12°C, the toxicity of both forms of PCP toD. g. mendotae andD. pulex did not differ significantly from that at 20°C; however, technical PCP was significantly more toxic toD. magna at 12°C for an exposure duration of 48 hr. There was no effect of test container size (100, 250, 600 and 1,000 mL) on the toxicity of PCP toD. magna at 20°C with the lower pH of 5.5, suggesting that adsorption to glassware was not a factor in availability of PCP to test organisms. Beaker size had no effect on the toxicity of PCP toD. pulex at 20°C with test solutions having a pH of 7.0-8.0.

Development of Suitable Test Methods for Evaluating the Toxicity of Contaminated Soils to a Battery of Plant Species Relevant to Soil Environments in Canada

Environment Canada and the Canadian Association of Petroleum Producers (CAPP) have embarked on a five year program to develop, standardize, and validate a battery of soil toxicity tests which can be used to assess the relative toxicity of contaminants in soils to terrestrial organisms. These tests must be applicable to soil conditions typically found in Canadian environments and the test species must be representative of the species of soil invertebrates or plants inhabiting soil ecosystems in Canada. Two of the tests being considered for development are a seed germination test and a seedling growth test using whole soils. The battery of plant species that is being considered for testing includes thirteen species representing six dicotyledonous families and 17 species representing two monocotyledonous families. The species of plants with one exception (Arabidopsis sp.) are representative of both above- and below-ground crop plants grown in agricultural lands across Canada, as well as non-crop plants that are also widely distributed in Canada. One of the objectives of the project is to screen 30 plant species and select ten species that are suitable for toxicity assessment of contaminated soils. In addition to selection of the most appropriate test species, research has focused on test method development. Comparison of toxicity test endpoints from reference tests permitted the assessment of the variation associated with each endpoint (root length, stem length, wet and dry mass of stem and root) for each species tested to date. The tests were performed using boric acid as the reference toxicant and an artificial soil and a field-collected reference soil as control soils. The methods and results from toxicity tests have been summarized and presented with recommendations regarding test species, methods, endpoints, and conditions.

Chronic toxicity of a pure and technical grade pentachlorophenol toDaphnia magna

Chronic toxicity test procedures (static, with renewal) were used to determine the chronic toxicity of sublethal concentrations of a technical formulation of pentachlorophenol (PCP) and pure pentachlorophenol toDaphnia magna. Test organisms 48+-12 h old were exposed for their entire lifespan (i.e., until death) to 0.01, 0.05, 0.1 and 0.5 mg technical PCP/L and 0.01, 0.087 and 0.1 mg pure PCP/L. Criteria used to assess chronic toxicity were mean time to appearance of the primiparous instar in the brood chamber, mean number of days to release of the first brood, mean number of broods produced per female, mean brood size per female, mean number of reproductive days, mean number of young produced per reproductive day per female and survivorship.Pentachlorophenol differentially affected maturation and reproduction but not survivorship or longevity. Mean number of broods produced per daphnid, length of the reproductive period, longevity and survivorship were insensitive criteria relative to mean time to appearance of the primiparous instar, time to release of first brood, brood size, and number of young produced per daphnid per reproductive day. Generally, there was little difference in toxicity of the three concentrations of pure PCP, for they significantly reduced mean brood size and rate of reproduction of young and significantly but differentially affected maturation.Technical PCP, at the highest concentration of 0.5 mg/L, significantly reduced mean brood size and the rate of production of young, and significantly delayed both time to appearance of the primiparous instar and release of the first brood. When differences in toxicity occurred, generally, pure PCP was more toxic than comparable concentrations of technical PCP. Although enhanced maturation was observed there was no compensatory reproduction.Similar conclusions regarding maturation and survivorship would have been derived from this study had it been terminated after the standard 21 d; however, the conclusions would have been different for reproduction. Only the highest concentration of technical PCP reduced brood size, the rate of production of young and total number of young produced per daphnid in 21 d. Only pure PCP at 0.05 mg/L caused daphnids to produce significantly fewer broods and, although the mean brood size was significantly larger than those in the controls, the mean number of young produced in 21 d was significantly reduced. These results differ substantially from those based on the entire life-cycle study and one of the most obvious differences is the much lower rates of young production in the entire life cycle study (2.41–3.03 young per daphnia per reproductive day) opposed to the first 21 days of the study (5.13–7.5 young per daphnia per reproductive day).

Quantitative weight of evidence assessment of higher-tier studies on the toxicity and risks of neonicotinoids in honeybees. 2. Imidacloprid

ABSTRACT A quantitative weight of evidence (QWoE) methodology was used to assess higher-tier studies on the effects of imidacloprid (IMI) on honeybees. Assessment endpoints were population size and viability of commercially managed bees and quantity of hive products. A colony-level no-observed-adverse effect concentration (NOAEC) of 25 µg IMI/kg syrup, equivalent to an oral no-observed-adverse-effect-dose of 7.3 ng/bee/d for all responses, was measured. The overall weight of evidence indicates that there is minimal risk to honeybees from exposure to IMI from its use as a seed treatment. Exposures via dusts from currently used seed coatings present a de minimis risk to honeybees when the route of exposure is via uptake in plants that are a source of pollen or nectar for honeybees. There were few higher-tier observational (ecoepidemiological) studies conducted with IMI. Considering all lines of evidence, the quality of the studies included in this analysis was variable, but the results of the studies were consistent and point to the same conclusion – that IMI had no adverse effects on viability of the honeybee colony. Thus, the overall conclusion is that IMI, as currently used as a seed treatment and with good agricultural practices, does not present a significant risk to honeybees at the level of the colony.

Quantitative weight of evidence assessment of higher-tier studies on the toxicity and risks of neonicotinoid insecticides in honeybees 1: Methods

ABSTRACT A quantitative weight of evidence (QWoE) methodology was developed and used to assess many higher-tier studies on the effects of three neonicotinoid insecticides: clothianidin (CTD), imidacloprid (IMI), and thiamethoxam (TMX) on honeybees. A general problem formulation, a conceptual model for exposures of honeybees, and an analysis plan were developed. A QWoE methodology was used to characterize the quality of the available studies from the literature and unpublished reports of studies conducted by or for the registrants. These higher-tier studies focused on the exposures of honeybees to neonicotinoids via several matrices as measured in the field as well as the effects in experimentally controlled field studies. Reports provided by Bayer Crop Protection and Syngenta Crop Protection and papers from the open literature were assessed in detail, using predefined criteria for quality and relevance to develop scores (on a relative scale of 0–4) to separate the higher-quality from lower-quality studies and those relevant from less-relevant results. The scores from the QWoEs were summarized graphically to illustrate the overall quality of the studies and their relevance. Through mean and standard errors, this method provided graphical and numerical indications of the quality and relevance of the responses observed in the studies and the uncertainty associated with these two metrics. All analyses were conducted transparently and the derivations of the scores were fully documented. The results of these analyses are presented in three companion papers and the QWoE analyses for each insecticide are presented in detailed supplemental information (SI) in these papers.

Quantitative weight of evidence assessment of higher tier studies on the toxicity and risks of neonicotinoids in honeybees. 4. Thiamethoxam

ABSTRACT A quantitative weight of evidence (QWoE) methodology was used to assess several higher-tier studies on the effects of thiamethoxam (TMX) on honeybees. Assessment endpoints were population size and viability of commercially managed honeybee colonies and quantity of hive products. A higher-tier field toxicology study indicated a no-observed-adverse effect concentration (NOAEC) of 29.5 µg TMX/kg syrup, equivalent to an oral no-observed-adverse-effect-dose (NOAED) of 8.6 ng/bee/day for all responses measured. For exposures via deposition of dust, a conservative no-observed-adverse-effect-rate at the level of the colony was 0.1 g TMX/ha. There was minimal risk to honeybees from exposure to TMX via nectar and pollen from its use as a seed-treatment. For exposures via dust and dust/seed applications, there were no concentrations above the risk values for TMX in nectar and pollen. Although some risks were identified for potential exposures via guttation fluid, this route of exposure is incomplete; no apparent adverse effects were observed in field studies. For exposures via dust/seed and dust/foliar applications, few adverse effects were observed. Considering all lines of evidence, the quality of the studies included in this analysis was variable. However, the results of the studies were consistent and point to the same conclusion. The overall weight of evidence based on many studies indicates that TMX has no adverse effects on viability or survival of the colony. Thus, the overall conclusion is that the treatment of seeds with thiamethoxam, as currently used in good agricultural practices, does not present a significant risk to honeybees at the level of the colony.

Quantitative weight of evidence assessment of risk to honeybee colonies from use of imidacloprid, clothianidin, and thiamethoxam as seed treatments: a postscript

ABSTRACT This paper is a postscript to the four companion papers in this issue of the Journal (Solomon and Stephenson 2017a, 2017b; Stephenson and Solomon 2017a, 2017b). The first paper in the series described the conceptual model and the methods of the QWoE process. The other three papers described the application of the QWoE process to studies on imidacloprid (IMI), clothianidin (CTD), and thiamethoxam (TMX). This postscript was written to summarize the utility of the methods used in the quantitative weight of evidence (QWoE), the overall relevance of the results, and the environmental implications of the findings. Hopefully, this will be helpful to others who wish to conduct QWoEs and use these methods in assessment of risks.

Response to Tennekes (2018) “The Resilience of the Beehive” Journal of Toxicology and Environmental Health B 20: 316–386

ABSTRACT This paper is a response to a letter from Dr. H Tennekes (“The Resilience of the Beehive” Journal of Toxicology and Environmental Health B 20: 316–386). Here we emphasize that our quantitative weight of evidence analyses were focused on the level of the honeybee colony. These colony-level responses include redundancy and resiliency as well as a number of possible sublethal effects of pesticides on the colony. We also note that the literature has shown that binding of neonicotinoid insecticides to the nicotinic acetylcholine receptor is reversible. The comments in this letter do not provide reasons to change our conclusions, that, as currently used in good agricultural practices as seed-treatments, imidacloprid, clothianidin, and thiamethoxam do not present significant risks to honeybees at the level of the colony.