The effect of creosote on the growth of an axenic culture of Myriophyllum spicatum L

Responses of soil microbial community and enzymes during plant-assisted biodegradation of di-(2-ethylhexyl) phthalate and pyrene

A pot experiment was conducted to explore the plant-assisted degradation efficiency of di-(2-ethylhexyl) phthalate (DEHP) and pyrene. Three plant species: Ceylon spinach, sunflower, and leaf mustard were cultivated in co-contaminated soils under three contamination levels: control (T0), 20 mg kg^-1 (T20), and 50 mg kg^-1 (T50). The results showed that a higher DEHP and pyrene degradation efficiency was observed evidently in planted cases, increasing from 42 to 53-59% (T0), 61 to 65-76% (T20) and 52 to 68-78% (T50) for DEHP, and from 22 to 30-49% (T0), 58 to 62-72% (T20), and 54 to 57-70% (T50) for pyrene. Under T20 contamination level, soil phospholipid fatty-acid analysis depicted the increased microbial biomass in rhizosphere, especially the arbuscular mycorrhizal fungus that is effective for the degradation of organic pollutants. The study also revealed that the activities of dehydrogenase, acid phosphomonoesterase, urease, and phenol oxidase negatively correlated with pollutant concentration. In general, the removal rate of DEHP and pyrene was highest in the soil planted with leaf mustard for each contamination level considered. For soils at T20 level, sunflower and leaf mustard appeared as interesting phytoremediation plants due to the improved removal rates of organic pollutants and the soil microbial activity.

Effects of toxicants with different modes of action on Myriophyllum spicatum in test systems with varying complexity

At the international workshop Aquatic Macrophyte Risk Assessment for Pesticides (AMRAP), it was noted that the EU risk assessment under the directive 91/414/EEC for herbicides, based only on algae and the monocotyledonous duckweed species Lemna sp., offers no certain protection against some growth regulating auxins. Therefore, AMRAP members proposed the introduction of the dicotyledonous water milfoil Myriophyllum as additional test species. This study was aimed to compare toxicity results from three test systems (TS) with varying complexity, namely Water TS, Sediment TS and Microcosm TS using Myriophyllum spicatum as test organism. As test substances, the photosynthesis inhibiting herbicide isoproturon, the growth regulating auxins fluroxypyr and 2,4-dichlorophenoxyacetic acid (2,4-D), and the non-specific acting toxicant 3,5-dichlorophenol (3,5-DCP) were chosen. It was assessed if and why the sensitivity of M. spicatum towards the four toxicants varied in the different test systems and if the addition of sucrose to the medium used in the Water TS had an effect on the sensitivity of Myriophyllum. All TS were suitable for detecting negative effects of toxicants with different modes of action on M. spicatum. The lowest variability of endpoints was found in the Water TS with lowest experimental complexity. For auxins, the endpoint weight did not result in robust EC50 values in all TS, whereas root related endpoints, which are also ecologically relevant, turned out to be very sensitive with low variance. Sucrose in the medium of the Water TS did not seem to influence the sensitivity of M. spicatum towards isoproturon and 3,5-DCP but may have increased the sensitivity of M. spicatum roots when exposed to 2,4-D. However, the findings of all TS resulted in similar risk estimations if root endpoints were not considered.

Toxicity of phenanthrene in freshwater sediments to the rooted submersed macrophyte, Vallisneria spiralis

A study was conducted to determine the response of the rooted submersed macrophyte, Vallisneria spiralis to phenanthrene in freshwater sediments with initial phenanthrene concentrations from 0 to 80 mg kg(-1) dry sediment. The sensitivity of various morphological endpoints was evaluated after 90 days of exposure. The most sensitive toxicity test endpoints were those that reflected root growth. Toxicological sensitivity of the endpoints changed with the effect level selected. The toxicity threshold from a plot of the EC(10) values was 1-2 orders of magnitude lower than those calculated for the threshold from plots of the EC(25) or EC(50) values. In addition, stimulatory responses (hormesis) on root growth were observed at subtoxic concentrations of phenanthrene, and a hormetic model should thus be incorporated for ecological risk assessment.

Sensitivity of submersed freshwater macrophytes and endpoints in laboratory toxicity tests

The toxicological sensitivity and variability of a range of macrophyte endpoints were statistically tested with data from chronic, non-axenic, macrophyte toxicity tests. Five submersed freshwater macrophytes, four pesticides/biocides and 13 endpoints were included in the statistical analyses. Root endpoints, reflecting root growth, were most sensitive in the toxicity tests, while endpoints relating to biomass, growth and shoot length were less sensitive. The endpoints with the lowest coefficients of variation were not necessarily the endpoints, which were toxicologically most sensitive. Differences in sensitivity were in the range of 10-1000 for different macrophyte-specific endpoints. No macrophyte species was consistently the most sensitive. Criteria to select endpoints in macrophyte toxicity tests should include toxicological sensitivity, variance and ecological relevance. Hence, macrophyte toxicity tests should comprise an array of endpoints, including very sensitive endpoints like those relating to root growth.

Growth of canola (Brassica napus) in the presence of plant growth-promoting bacteria and either copper or polycyclic aromatic hydrocarbons

Growth of canola (Brassica napus) seeds treated with plant growth-promoting bacteria in copper-contaminated and polycyclic aromatic hydrocarbon (PAH)-contaminated soils was monitored. Pseudomonas asplenii AC, isolated from PAH-contaminated soil, was transformed to express a bacterial gene encoding 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and both native and transformed bacteria were tested for growth promotion. Inoculation of seeds, grown in the presence of copper or creosote, with either native or transformed P. asplenii AC significantly increased root and shoot biomass. Native and transformed P. asplenii AC and transformed P. asplenii AC encapsulated in alginate were equally effective at promoting plant growth in copper-contaminated soils. In creosote-contaminated soils the native bacterium was the least effective, and the transformed encapsulated bacterium was the most effective in growth promotion.Key words: plant growth-promoting bacteria, phytoremediation, copper, polycyclic aromatic hydrocarbons, Brassica napus, ethylene, alginate encapsulation.

Haloacetic acids in the aquatic environment. Part I: macrophyte toxicity

Haloacetic acids (HAAs) are contaminants of aquatic ecosystems with numerous sources, both anthropogenic and natural. The toxicity of HAAs to aquatic plants is generally uncharacterized. Laboratory tests were conducted with three macrophytes (Lemna gibba, Myriophyllum sibiricum and Myriophyllum spicatum) to assess the toxicity of five HAAs. Myriophyllum spp. has been proposed as required test species for pesticide registration in North America, but few studies have been conducted under standard test conditions. The HAAs in the present experiments were monochloroacetic acid (MCA), dichloroacetic acid (DCA), trichloroacetic acid (TCA), trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA). MCA was the most toxic to Myriophyllum spp. with EC50 values ranging from 8 to 12.4 mg/l depending on the endpoint, followed by DCA (EC50 range 62-722.5 mg/l), TCA (EC50 range 49.5-1702.6 mg/l), CDFA (EC50 range 105.3 to >10,000 mg/l) and with TFA (EC50 range 222.1 to 10,000 mg/l) the least toxic. Generally, L. gibba was less sensitive to HAA toxicity than Myriophyllum spp., with the difference in toxicity between them approximately threefold. The range of toxicity within Myriophyllum spp. was normally less than twofold. Statistically, plant length and node number were the most sensitive endpoints as they had the lowest observed coefficients of variation, but they were not the most sensitive to HAA toxicity. Toxicological sensitivity of endpoints varied depending on the measure of effect chosen and the HAA, with morphological endpoints usually an order of magnitude more sensitive than pigments for all plant species. Overall, mass and root measures tended to be the most sensitive indicators of HAA toxicity. The data from this paper were subsequently used in an ecological risk assessment for HAAs and aquatic plants. The assessment found HAAs to be of low risk to aquatic macrophytes and the results are described in the second manuscript of this series.

Trichloroacetic acid fate and toxicity to the macrophytes Myriophyllum spicatum and Myriophyllum sibiricum under field conditions

Trichloroacetic acid (TCA) has been detected in rain, snow, and river samples throughout the world. It may enter into natural water systems via herbicide use, as a by-product of water disinfection, from emissions of spent bleach liquor of kraft pulp mills, and as a natural fungal product. This compound is phytotoxic and likely to accumulate in aquatic environments. A study to assess the fate of TCA in semi-natural aquatic environments and the toxicity of TCA to rooted aquatic macrophytes was conducted. The experiment involved exposing three replicate 12000 l aquatic microcosms at the University of Guelph Microcosm Facility to 0.05, 0.5, 3, and 10 mg/l of TCA for 35 days in a one-way analysis of variance design. Each microcosm was stocked with 14 individual 5 cm apical shoots of Myriophyllum spicatum and M. sibiricum. The plants were sampled at regular intervals and assessed for the somatic endpoints of plant length, root growth, number of nodes and wet and dry mass and the biochemical endpoints of chlorophyll-a and chlorophyll-b, carotenoid content, and citric acid levels. TCA half-lives in the microcosms ranged from 190 to 296 h depending on the initial concentration of TCA. Myriophyllum spp. results indicate that while there were some statistically significant differences from controls, there were no biologically significant effects of TCA for any of the endpoints examined. These data suggest that TCA does not pose a significant risk to these macrophytes up to 10 mg/l, which typically exceeds environmentally relevant concentrations by several orders of magnitude.

The effect of creosote on membrane ion leakage in Myriophyllum spicatum L

Creosote is a complex chemical mixture used as a wood preservative that has the potential to contaminate aquatic systems via spills or leaching from treated wood structures. Aquatic macrophytes are important components of aquatic systems, which may be adversely affected by creosote contamination. Several chemicals that are constituents of creosote are known to affect cell membranes in various organisms. Therefore, the effect of creosote on the membrane permeability of the aquatic macrophyte Myriophyllum spicatum was investigated. Apical meristems from axenic Myriophyllum plants were exposed for 4 days to 8 creosote treatments (ranging from 0.1 to 92 mg creosote/l) plus controls. Following the exposure, the ion leakage from the cellular membranes was determined via conductivity measurements. The concentration of 15 polycyclic aromatic hydrocarbons (PAHs) in the growth medium and in the plant tissue was also determined. A significant increase in ion leakage was observed at all creosote concentrations, even those in which no biological effects were observed on plant growth. However, saturation of the growth medium with PAHs was observed, thus indicating that nominal creosote concentrations may over-estimate the actual exposure.