R. J. Maguire

Fate and ecotoxicity of the new antifouling compound irgarol 1051 in the aquatic environment

Residue analyses and ecotoxicity assessment were conducted on the new antifouling compound Irgarol 1051 (2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine) and its degradation product M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) in order to delineate the environmental fate and impact of Irgarol 1051 on the aquatic ecosystem. For the first time, the Irgarol degradation product (M1) was positively identified in environmental samples. During the 1998 Irgarol survey, concentrations of M1 (up to 1870 ng/l) were generally higher than those of Irgarol in the coastal waters of the Seto Inland Sea in Japan, suggesting a greater environmental persistence for M1 than for the parent compound Irgarol 1051 in the aquatic ecosystem. Ecotoxicity testing revealed that Irgarol 1051 and M1 were moderately toxic to a marine bacterium and the four crustaceans tested, but were highly toxic to some algae and higher plants. In the root elongation inhibition bioassay, M1 showed a phytotoxicity at least 10 times greater than that of Irgarol and six other triazine herbicides (terbutryn, terbutylazine, terbumeton, simetryn, atrazine and simazine). These results strongly suggest that both Irgarol 1051 and its persistent degradation product M1 may potentially affect and/or damage the primary producer community in aquatic ecosystems. To safeguard the aquatic ecosystem from the damaging impact of micro contaminants, it is recommended that, besides monitoring for the target parent compound, major degradation products should also be included in environmental surveys. Otherwise, there is a risk of underestimating the ultimate impact of a particular toxicant on the environment.

Transformation of the new antifouling compound Irgarol 1051 by Phanerochaete chrysosporium

Irgarol 1051, 2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine, is a newly developed herbicidal additive for use in copper-based antifouling paints. It is intended to replace the antifouling agent tributyltin, which has been regulated internationally due to its severe impact on the aquatic ecosystem. However, there is no information in the open literature on the persistence and degradation of Irgarol, a fact that hinders the assessment of its ultimate impact on the environment. This study showed that the white rot fungus Phanerochaete chrysosporium was capable of biotransforming Irgarol 1051. It appears that the metabolism of Irgarol by the fungus proceeds mainly via partial N-dealkylation. Metabolic dealkylation occurs at the cyclopropylamino group resulting in metabolite M1, which has tentatively been identified as 2-methylthio-4-tert-butylamino-6-amino-s-triazine. M1 appeared to be a stable and/or terminal metabolite. No evidence of the heterocyclic ring cleavage of Irgarol 1051 was observed, thus implying a possibility of its degradation product(s) accumulating in the environment.

Cohesive sediment transport: emerging issues for toxic chemical management

The association of many environmentally sensitive chemicals and their transformation products with mineral and organic substrates is of considerable importance for environmental monitoring, prediction and management purposes in rivers and their basins. Our understanding of these relationships is poor. This paper reviews processes of particular concern, including the physical behaviour of fine-grained (< 63 µm) sediment in freshwater; the role of flocculation as a transport vector; the processes that control freshwater flocculation including microbiological factors; the uncertainty in conventional sediment transport models for predicting pathways of sediment-associated chemistry; the relationship between suspended sediment and toxicity in the water column; and the partitioning of chemicals between the sediment, organic and water phase, including the significance of these in predicting chemical transport on suspended matter.

Mercuric chloride-catalyzed hydrolysis of the new antifouling compound irgarol 1051

Irgarol 1051, 2-methylthio-4-tert-butylamino-6-cyclopropylamino-s-triazine, is a newly developed herbicidal additive for use in copper-based antifouling paints. It is intended to replace the antifouling agent tributyltin, which has been regulated internationally due to its severe impact on the aquatic ecosystem. However, there is no information in the open literature on the abiotic degradation of Irgarol, a fact that hinders the assessment of its ultimate impact on the environment. This study showed that mercuric chloride was capable of rapidly catalyzing the hydrolysis of Irgarol 1051 in distilled water and buffer solutions. The degradation appeared to follow the reaction of a catalyzed hydrolysis and was not significantly affected by the pH tested (5 to 9). All other 5 heavy metal salts tested (AgNO3, CdCl2, CuSO4, PbCl2 and ZnCl2) had practically no catalytic property on Irgarol hydrolysis, implying the involvement of a specific activity for Hg2+ in this reaction. The mechanism for the catalyzed hydrolysis may be the formation of bidentate chelation through nitrogen (No. 5) on the ring and the nitrogen on the cyclopropylamino side chain in Irgarol 1051 with the Hg2+ ion. The resulting four-member chelate complex would weaken the cyclopropyl-amino bond considerably, thus facilitating the hydrolysis reaction. Ultraviolet spectroscopy of the reaction mixtures and the identification of Irgarol hydrolysis product M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) by GC-MS and LC-MS provided the basis for the proposed mechanism on the HgCl2-catalyzed hydrolysis of Irgarol 1051. M1 appeared to be more stable than the parent compound Irgarol 1051, thus implying its possible accumulation in the environment. One practical aspect of this work is that HgCl2 should not be used in preserving water samples in Irgarol 1051 monitoring programs.

Factors affecting chemical biodegradation

Microbial degradation is one of the most important processes responsible for the removal of chemical contaminants from the environment. Since the aquatic compartment is frequently the ultimate depository for many man‐made substances, there is a need to understand factors that control and/or affect the rate of biodegradation for chemical substances in the aquatic environment. In this study, several priority chemicals encompassing various biocides (2,4‐dichlorophenoxy acetic acid, carbaryl, fenitrothion, pentachlorophenol) and a nitroaromatic (2,4‐dinitrotoluene) were assessed for their biodegradability in cyclone fermentors under aerobic and anaerobic conditions, with and without co‐metabolites. Among those factors investigated, aerobic and anaerobic conditions, availability of co‐metabolites, and pre‐exposure of microorganisms to the test chemical were found to be the most significant elements in controlling the rate of biodegradation. Other factors (e.g., acclimation period) requiring attention in calculating the rate of biodegradation were also discussed. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 476–483, 2000

Volatilization of metolachlor from water

Abstract The volatilization of metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐l‐methylethyl)acetamide]from water was studied in the laboratory and in an outdoor open‐channel experiment. As expected, volatilization was not significant at temperatures ≤ 25 °C. However, at temperatures ≥ 30 °C, there was significant volatilization (e.g., half‐life of 20 days at 40 °C in unstirred solutions). This increased volatility reflected the rapid increase of the Henrys law constant with temperature. Additional experiments indicated that aeration of water significantly accelerated volatilization losses. Such air‐stripping may be important in very turbulent streams and rivers and when water flows over hydraulic structures such as weirs. The experiments reported here indicate the importance that ecosystem‐specific characteristics can have on the persistence of environmental contaminants.

Microbial adsorption of cyanazine and metolachlor

A laboratory experiment was performed to study the role of microorganisms in producing the non-extractable residues by anaerobically incubating cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5,-triazin-2-yl]-amino]-2-methoxy -l- methylethyl)acetamide] and metolachlor [2-chloro-N-(2-ethyl-6-methoxy-l- methylethyl)acetamide] in culture media that had been inoculated with sewage bacteria from anaerobic sludge. Based on the gas chromatographic analyses of extracts from the degradation, adsorption, and abiotic controls for the parent herbicide and its possible metabolites, this study provided the first direct evidence that bacterial biomass, rather than metabolism, was mainly involved in the formation of bound residues with cyanazine. Anaerobic bacteria appeared to be incapable of forming bound residues with metolachlor. The common phenomenon of age-dependent extractability for bound residues was observed with cyanazine. These results imply that bacteria may adsorb pesticides selectively with preference for certain chemical structures over others.

Assessment of cyanazine persistence in water

Cyanazine (2-[[4-chloro-6-(ethylamino)-1,3,5,-triazin-2-yl]-amino]-2-methylpropanenitrile) is an important selective herbicide used for the control of several annual grassy weeds and certain broad-leafed weeds in fields of corn, soybeans, and triazine-resistant canola. It is one of the most heavily used agricultural herbicides in Ontario. There is, however, very little information in the open literature on the aquatic fate and persistence of cyanazine, a fact that hinders the assessment of its ultimate impact on the aquatic ecosystem. This research showed that cyanazine was very stable in natural surface runoff and soil leachate. It was also very resistant to microbial degradation in water under both aerobic and anaerobic conditions. No apparent biodegradation or biotransformation of cyanazine was observed in a test using mixed cocktails of farmland runoff and soil leachate after an incubation period of 98 days. Its biological persistence was further demonstrated by a cyclone fermentor study in which cyanazine was found to be totally immune to the biodegradation potential of a polynuclear aromatic hydrocarbon degrading bacterial culture and sewage microorganisms after an incubation period of 110–195 days. Using the herbicide metolachlor as a biodegradability reference compound and the white rot fungus Phanerochaete chrysosporiumas the test organism, cyanazine was estimated to have a persistence in water much greater than that of metolachlor. Thus, the extensive herbicidal use of cyanazine may have a long-lasting impact on Canadian aquatic ecosystems.