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1989 - 1994

Occurrence and fate of selected agricultural pesticides in water and sediments of Lake Erie coastal marshes

J.A. Millette1, B.P. Bourgoin2 (in memoriam), A. Mudroch2, K.E. Day2, D.S. Gamble1,
D.W. Gutzman1 , E. Topp1 , L. Emili3 , R. Roshon4

1Land Resource Division, Centre for Land & Biological Resources Research, Agriculture and Agri-Food Canada, Research Branch, Ottawa, Ontario K1A 0C6
2National Water Research Institute, Environment Canada , Burlington, Ontario
3McMaster University, Hamilton, Ontario
4University of Guelph, Guelph, Ontario

July 5, 1994

Download report  (726 KB pdf)   [graphs & tables included]

1. Rationale and objectives

With continued application of pesticides in the Great Lakes basin, nonpoint source pollution of nearshore wetlands is becoming a major concern. Unlike point sources of contamination such as at the outlet of an effluent pipe, nonpoint sources are more difficult to define. An estimated 21 million kg of pesticides are used annually on agricultural crops in the Canadian and American Great Lakes Watershed (GAO 1993). Herbicides account for about 75% of this. These pesticides are frequently transported via sediment, ground or surface water flow from agricultural land into the aquatic ecosystem. With mounting concerns and evidence of the effects of certain pesticides on wildlife and human health (Colborn et al. 1993), it is crucial that we determine the occurrence and fate of agricultural pesticides in sediments found in marshes draining into the Great Lakes.

Limited information exists on contamination of sediments by contemporary agricultural pesticides. Transport of pesticides adsorbed to particulate material may be an important mechanism in pesticide movement from agricultural land to fresh water systems. The deposition of pesticide-carrying particulates could potentially contaminate sediments. The extent of sediment contamination caused by pesticides and the fate of pesticides in sediments in near-shore marshes is unclear. Furthermore, there have been very few studies in agricultural watersheds which address the question of bioavailability and, thus, toxicity of pesticides to organisms which live in or near sediments.

A multidisciplinary study was initiated to assess nonpoint source contaminant transport from agricultural land into near-shore zones and wetlands of the Great Lakes Basin. A region located in Essex County of southwestern Ontario was selected due to its extensive agricultural land use, encompassing more than 2200 farms (OMAF 1993), and due to the presence of environmentally sensitive marshes adjacent to Lake Erie.

The objectives of the study were 1) to examine selected near-shore and wetland locations in the Canadian Great Lakes Basin, and agricultural sources of sediments contaminated by toxic agricultural chemicals (esp. pesticides); 2) estimate the quantity of chemicals present; 3) evaluate their bioavailability and impact on wetland ecology; and 4) identify the options for remedial action.

This report summarizes some of the data collected during the life of the study. Unfortunately, it is not possible to include all of the detailed data on sediment quality until the authors have had some time to interpret the results. A separate report is being prepared on sediments that were sampled from the areas studied. Additional scientific papers and presentations will be prepared by the authors to communicate the results of our study.

4. Conclusion

Field results indicate that some pesticides appear to be released from soil or sediment particles over a time scale of years. Pesticides applied in this watershed appear to have long-term and cumulative effects within the boundaries of the watershed. This is consistent with chemical binding studies which indicate slow diffusion of pesticides into and out of soil/sediment particles. Of those monitored, trifluralin and metolachlor were the only pesticides detected in sediments. The reasons for this are not yet clear. Ecotoxicological studies showed contaminant levels in sediment samples to be below those necessary to have a significant effect on benthic invertebrates. Some toxic effect on plants, especially algae was noted, however. Although the relation was not conclusively demonstrated, some pesticides (particularly triazines) were measured in water samples at concentrations known to cause a detrimental effect. The low strength of binding to sediments observed for some pesticides implies that they remain largely in the more bioavailable "free" form. This limits accumulation in sediments, but may enhance transport into the Great Lakes. The presence of atrazine-degrading microorganisms in sediments may reduce the amount of this herbicide transported.

5. New Technologies and Benefits

Several bioassays which have not been previously used to determine the toxicity of sediment samples from agricultural watersheds were developed and used in this study. The toxicity test with invertebrates measures reproductive effort and therefore is very useful in the determination of chronic toxicity. The rooted macrophyte bioassay is an innovative technique under development at the University of Guelph and was used for the first time in the field scenario.

New methods of extracting pesticides from water samples were tested. The technique using solid phase extraction discs was shown to effectively recover pesticides from water without the need for the large volumes of high purity solvents required by traditional methods (Triska et al.1994).

The HPLC micro-filtration method to versatile and was applied to sediments for the first time. It was observed that similar binding mechanisms apply to soils and sediments.

Microorganisms capable of mineralizing atrazine completely were discovered in Essex County sediments (Topp et al 1994). This clearly offers potential benefits for farmers and environmentalists. To take maximum advantage of this, we must find ways of increasing the residence time of pesticides in wetland sediments.

6. Implications for Great Lakes Ecosystem

Most of the research was conducted on two watersheds. However, the uniform conditions existing in Essex County likely allow extrapolation to other watersheds and marsh areas along Lake Erie and Lake St. Clair. Chemical speciation studies were conducted on two widely applied herbicides: atrazine and metolachlor.

The lack of contamination of sediments with pesticides in agricultural watersheds is encouraging with regards to the minimal toxic effect on benthic invertebrates. However, this does not preclude contamination of marshland water. The growth of two species of plants was inhibited when placed in water samples collected following rainfall events. Although this water was found to contain herbicides ( atrazine, simazine, metribuzin) which are known to inhibit photosynthesis (Day 1993), this relationship has yet to be confirmed.

Microorganisms in sediments having the ability to rapidly degrade atrazine may reduce environmental contamination with this herbicide. This potential could be exploited in managed drainage systems for ensuring that atrazine loss from agricultural areas does not enter the Great Lakes system.

Greater farmer participation in the process is encouraged so that they can understand why the research is done. Some farmers that were interviewed were skeptical and refused to answer questions pertaining to their agricultural practices.

7. Technology transfer potential

  • Atrazine mineralizing microorganisms for bioremediation

  • HPLC micro-filtration technique for chemical speciation

  • The "battery of bioassay tests" approach to ecotoxicological evaluation of water and sediments

8. Gaps/needs for future research

  • More bioassays with additional species of aquatic plants especially rooted macrophytes

  • Field assessment of the impact of herbicides on aquatic plant species in wetlands

  • Information on the impact of pesticides on amphibians and reptiles

  • Quantification of the transport of pesticides in water and sediments moving down a watershed and application of watershed models (ILWIS, AGNPS)

  • Evaluation of groundwater quality and movement in watersheds

  • Extension of chemical speciation to other pesticides such as trifluralin and metribuzin

  • Examination of the degradation of other herbicides in sediments

  • Assessment of the biodegradation of pesticides under field conditions in natural and constructed drainage systems designed to reduce off farm movement of agrochemicals.



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