Hans G. Peterson

Aquatic phyto-toxicity of 23 pesticides applied at expected environmental concentrations

Abstract Environment Canada uses an Expected Environmental Concentration (EEC) in evaluating the hazard of pesticides to nontarget aquatic organisms. This concentration is calculated by assuming an overspray of a 15 cm deep waterbody at the label application rate. The EEC of pesticides is then related to the EC50 (concentration causing a 50% reduction in a chosen toxicity endpoint) for a given aquatic test organism. At present, the use of an uncertainty factor is suggested in the literature if only a few species are tested because of important interspecific differences in pesticide sensitivity. The phytotoxicity of the EEC of 23 different pesticides to ten algae (24 h inhibition of 14C uptake) and one vascular plant (7-day growth inhibition) was determined in an effort to examine the question of interspecific sensitivity and its relation to the development of pesticide registration guidelines. Chemicals included five triazine herbicides (atrazine, cyanazine, hexazinone, metribuzin, and simazine), four sulfonylurea herbicides (chlorsulfuron, metsulfuron-methyl, ethametsulfuron-methyl, triasulfuron), two phenoxyalkane herbicides (2,4-D and MCPA), two pyridine herbicides (picloram and triclopyr), a substituted urea, an amine derivative, and an imidazolinone herbicide (tebuthiuron, glyphosate and imazethapyr, respectively), a bipyridylium (diquat), a hydroxybenxonitrile (bromoxynil), an aldehyde (acrolein) and an acetanilide (metolachlor) herbicide, as well as two carbamate insecticides (carbofuran and carbaryl) and a triazole derivative fungicide (propiconazole). Test organisms were selected based on ecological relevance and present use in test protocols. Organisms included green algae (Scenedesmus quadricauda and Selenastrum capricornutum), diatoms (Nitzschia sp. and Cyclotella meneghiana), cyanobacteria (Microcystis aeruginosa, Oscillatoria sp., Pseudoanabaena sp., Anabaena inaequalis and Aphanizomenon flos-aquae) and a floating vascular plant, duckweed (Lemna minor). The five triazine herbicides, acrolein and diquat inhibited the carbon uptake of all algae, diatoms and cyanobacteria by more than 50%. Two other pesticides, carbaryl and tebuthiuron, caused more than 50% inhibition in 90% of the algae tested. Nine of the 23 pesticides, five of which were triazine herbicides, were therefore highly phytotoxic to algae. Twelve pesticides inhibited growth of duckweed by more than 50%. Once again, all five of the triazine herbicides were among this group, as well as three sulfonylurea herbicides and acrolein, diquat, metolachlor and tebuthiuron. Duckweed was the most sensitive organism tested, being equally affected by all pesticides causing algal phytotoxicity (with the exception of carbaryl), as well as being acutely affected by sulfonylurea herbicides. Green algae were least sensitive to diquat; diatoms and one cyanobacterium were the only organisms that showed sensitivity to glyphosate. Through testing the phytotoxicity of a variety of agricultural pesticides to a wide range of algal taxa, it is evident that there are considerable differences in sensitivity among species and that the use of an uncertainty factor is necessary to provide an acceptable margin of safety in evaluating the hazard presented by these chemicals to the aquatic environment.

Physiological toxicity, cell membrane damage and the release of dissolved organic carbon and geosmin by Aphanizomenon flos-aquae after exposure to water treatment chemicals

Reducing the level of dissolved organic carbon is an increasingly important goal in the treatment of drinking water. Dissolved organic carbon (DOC) compounds react with chemical disinfectants to form undesirable by-products, and DOC provides a substrate for bacterial growth. Chemicals used in water treatment processes and surface water reservoir management can cause the release of dissolved organics from photosynthetic aquatic organisms, and specific organic compounds can impart taste, odour and sometimes toxicity to treated water. Thus, chemical treatment of water may exacerbate the problem of dissolved organic carbon loading. The effects of several chemicals used at different stages of the water treatment process were studied on a nitrogen-fixing strain of the cyanobacterium Aphanizomenon flos-aquae. Chemicals included chlorine, potassium permanganate, aluminum sulphate, ferric chloride, calcium hydroxide, hydrogen peroxide and copper sulphate. Physiological effects on Aphanizomenon, as quantified by its ability to fix nitrogen, were compared with cell membrane damage (manifested as potassium release) and the release of organic cellular components, including DOC and the specific odour compound, geosmin. Aluminum sulphate and ferric chloride did not cause either physiological toxicity, cell membrane damage or the release of DOC at treatment usage concentrations. Calcium hydroxide at low levels and hydrogen peroxide caused physiological toxicity, but only limited membrane damage, DOC and geosmin release. Chlorine, copper sulphate and potassium permanganate caused physiological damage with concomitant release of both DOC and geosmin at concentrations lower than those currently used in water treatment. Consequently, these last three chemicals create potential water treatment problems by releasing DOC and specific problem compounds.

Toxicity of hexazinone and diquat to green algae, diatoms, cyanobacteria and duckweed

Abstract Hexazinone and diquat are two broad-spectrum contact herbicides used in a variety of crop and non-crop applications. Both pesticides are highly water soluble and persistent in the aquatic system. Hexazinone is mobile in soil and, thus, the potential for leaching into ground water and for overland runoff into surface water is high; diquat, however, is rapidly bound by soil and sediment to a biologically inactive form, at least temporarily. Toxicity to green algae (two species), diatoms (two species) and cyanobacteria (five species) was determined using inhibition of 14 C uptake. Toxicity to the floating vascular plant, duckweed, was tested by measuring seven-day growth inhibition. Test organisms exhibited large differences in sensitivity to both herbicides. The green algae, diatoms, and duckweed (all eukaryotes) were more sensitive to hexazinone than were cyanobacteria (prokaryotes). Mean concentrations at which 50% inhibition occurred in these groups were 0.01 (green algae), 0.05 (diatoms), 0.07 (duckweed), and 0.6 (cyanobacteria) mg hexazinone per litre, respectively. In contrast, green algae were comparatively tolerant of diquat (EC 50 values approximately 0.6 mg l −1 ), while the cyanobacteria and diatoms were much more sensitive (mean EC 50 values of 0.074 and 0.079 mg diquat per litre). Duckweed showed the greatest sensitivity to diquat, with 50% inhibition of growth occurring at 0.004 mg l −1 . That some non-target aquatic plants are susceptible to diquat toxicity at less than 0.01 mg l −1 is significant, as most methods of diquat analysis have minimum detection limits of 0.01 to 0.05 mg l −1 . Therefore, algae and vascular aquatic plants may suffer phytotoxic effects in a contaminated water body even when diquat is undetectable chemically. Differential sensitivity to herbicide contaminants among taxonomic groups of plants may have ecological consequences. Cyanobacteria may produce neuro- and hepato-toxins and constitute a poor food resource for higher trophic levels relative to the other organisms tested. Contamination of surface water with hexazinone may degrade water quality for wildlife, both by causing food reduction and habitat loss through inhibition of green algae, diatoms and macrophytes, and by allowing the proliferation of cyanobacteria. Varying responses among the different test algae to the two herbicides under study indicated that a wide taxonomic range of test species is necessary in evaluating the impacts of contaminants in aquatic systems.

Disinfection by-product formation after biologically assisted GAC treatment of water supplies with different bromide and DOC content

Abstract Chlorination of drinking water in the presence of bromide and dissolved organic carbon (DOC) leads to the formation of brominated and chlorinated disinfection by-products (DBP). The concentration of bromide ions in the raw water is a significant factor in the speciation of DBP formed, and causes shifts in trihalomethane (THM) formation from chlorinated to brominated species. Drinking water treatment techniques that remove organic contaminants without affecting bromide ion concentrations cause increases in the brominated THM. For the present study, three water supplies containing different DOC and ambient bromide concentrations were filtered through biologically assisted granular activated carbon (BGAC). Similar to adsorption and coagulation treatment, this treatment does not remove bromide from drinking water; also, THMFP (trihalomethane formation potential) analysis indicated that the chlorinated effluent contained higher concentrations of brominated THM in comparison to the influent. Although BGAC may increase the brominated THM, which may be more toxic than the chlorinated THM, the overall reduction of THMFP by DOC removal far exceeds this negative change, thereby producing a much less toxic finished drinking water. This work is part of a study to make high DOC surface waters on the Canadian prairie safe and palatable for small volume users (individuals or small communities).

Trihalomethanes in finished drinking water in relation to dissolved organic carbon and treatment process for Alberta surface waters

Abstract Disinfection by‐products are formed when the disinfectant (often a strong oxidizer) reacts with bulk dissolved organics in the water during treatment and distribution. The relationship between trihalomethanes (THMs) and bulk dissolved organics (DOC) in the finished drinking water for municipal treatment plants in Alberta using surface waters has been summarized. Treatment processes considered included chlorination with filtration alone, chlorination with complete treatment (coagulation, sedimentation and filtration [CSF], with or without additional treatment such as aeration and activated carbon), and chloramination with CSF. Trihalomethane levels were significantly correlated with the content of DOC as would be expected. For complete treatment systems using chlorination, the average THM yield was approximately 11 μg THM per mg of DOC. These data suggest that if the DOC level of the treated water exceeds 4 mg L‐1, the average THM will likely exceed 50 ug L‘1 if chlorination is used. For chloramin...

A New Kinetic Model for 4-Chlorophenol Adsorption on Expanded Clay

The adsorption of 4-chlorophenol on an expanded commercial clay used in water purification has been studied. Experiments using 4-chlorophenol concentrations of 50, 100, 250, 500, 750, 1000, 1250 and 1500 mg L-1 were carried out in column reactors at 25ºC.A new adsorption kinetics equation has been developed based on the equation for the variation in solute concentration in the liquid phase, representing the difference between the adsorption rate minus the desorption rate that at equilibrium represents the Langmuir isotherm. This was used to derive a new finite equation for the development of the adsorption curve.

Algal Microplate Toxicity Test Suitable for Heavy Metals

This test method was specifically designed to assess phytotoxicity of samples containing heavy metals (synthetic solutions, effluents, elutriates, leachates). Metal toxicity can be greatly affected by media composition and by changes caused by algal growth, such as the increase in pH and the release of dissolved organics. These problems can be severe in many test systems, but have been minimized in the procedures described here. The testing specifically addresses the following: • Metal complexing compounds, which can affect toxicity, have been reduced or eliminated from the test media. • Short duration testing results in small increases in algal biomass causing no significant changes in prevailing environmental conditions (pH, production of organics, etc.). • A battery of test organisms, varying in morphology, nutrient requirements and ecological relevance is used. • A microplate format makes the test cost, space and time effective.