Fact Sheet April, 2002

The Lead Shot Shaker

A Device for Remediating Lead Shot-Contaminated Sediment

 Severn Sound Environmental Association 

 Project Partners included: Great Lakes Sustainability Fund, TD Friends of the Environment, Wye Marsh Wildlife Centre                   

Every year in North America , thousands of ducks and other waterbirds die or suffer sublethal effects from lead poisoning (CWS, 1998).  Lead poisoning in waterfowl, including ducks, geese and swans, can be caused by ingestion of lead pellets (Scheuhammer and Norris, 1995).  Spent lead pellets (shot) in wetlands are a result of hunting activities over water, and birds can mistake the residual lead shot for food items or as a source of grit which aids in digestion.  When ingested, the grinding action in the gizzard and acidic conditions in the digestive system cause the pellets to breakdown and lead is released into the bloodstream; the lead is then carried throughout the body and accumulates in the bones and vital organs, such as the kidneys, liver, and brain, causing lead poisoning (CWS, 1998).  In an effort to reduce the incidence of lead poisoning in waterfowl by ingesting lead shot, Canada implemented bans restricting the use of lead shot for hunting.  Although an effective lead shot ban will eliminate the supply of additional lead pellets to wetlands, it does not address the issue of pre-ban pellets remaining in sediment at a depth accessible to foraging waterfowl.

In 1991, the Friends of Wye Marsh Inc. began releasing Trumpeter Swans (Cygnus buccinator) into Wye Marsh, near Midland , Ontario , as part of a provincial reintroduction program.  Although lead shot was not initially a concern for the program, within the first four years, more than a dozen of the 75 released Trumpeter Swans developed lead poisoning.  Remnant lead shot has seriously impacted the success of the reintroduction effort: despite successful initial treatment in some cases, the mortality rate was high in the long term, and many swans died before successfully producing offspring.  The Lead Shot Remediation Project, a cooperative program between the Friends of Wye Marsh and the Severn Sound Remedial Action Plan, was initiated in the Severn Sound watershed in 1994 in an effort to decrease the risk of Wye Marsh Trumpeter Swans and other waterfowl ingesting remnant lead shot.  The project was initiated with financial and technical support from Environment Canada’s Great Lakes 2000 Cleanup/Sustainability Fund.

Description of Remedial Technology

After two years of research, a prototype of remedial technology, in the form of a vibration device, was developed to sink remnant lead pellets beyond the range of availability for most waterfowl, with minimal impacts on the surrounding environment.  Vibration induces the pellets to move downward through the sediment, a process which naturally occurs at a much slower rate through the production and release of methane gas. 

Extensive laboratory and field testing had proven that the vibration device was effective in sinking pellets 17 centimetres (6.6") into soft surficial sediments.  Based on the project findings, an improved mechanical vibrator, the Lead Shot Shaker, was built by Normrock Industries Inc.  The revised prototype resembles a cultivator, with a series of tempered steel rods 71 cm (28") long, and is approximately 1 m wide by 1 m long (39" by 39").  The rods, which enhance the vibration, are lowered into the sediment to a depth of approximately 25 cm (10") and are vibrated by a hydraulic motor.  Water depths between 40 cm and 1.1 m (16" and 42") are optimal for remediation.  The delivery platform for the Lead Shot Shaker is a steel barge 3 m x 6m x 60 cm (10' x 20' x 24"), which facilitates travel between areas to be treated with a minimum of wetland disturbance.  It requires a minimum of 30 cm (12") water depth to float, and maintains its working position with side stabilizers which act as anchors in the sediment.  The barge is also equipped with an emergency spill kit with a sorbent capacity of 240 litres (63.4 US gal), and includes oil sorbent booms and sheets, plugging compound, and safety gear.  The Shot Shaker is attached to the front of the barge by a mini-excavator arm that allows it to be moved in and out of the sediment in an arc.  The maximum operating depth of the arm is 1.5-1.8 m (5-6').  The hydraulics for the arm and propeller operate on biodegradable vegetable-based hydraulic fluid, and are powered by a 30 H.P. Lombardini Diesel engine (LDW 903) mounted on the rear of the barge.  The hydraulically-driven propeller can be raised in shallow water to protect aquatic vegetation and prevent sediment disturbance.

Implementation & Effectiveness

Lead pellets are very small and dispersed over a fairly broad area in any given wetland.  The Shot Shaker was applied to ‘hot spots’ in Severn Sound.  These ‘hot spots’ are areas of high potential for lead shot accumulation, such as areas that were historically popular for hunting and adjacent to identified hunting blinds, which are also feeding areas for waterfowl such as Trumpeter Swans.  The remediation device was utilized at specific sites within the Wye Marsh Provincial Wildlife Area and Hog Bay coastal wetland, near Port McNicoll, Ontario .  The Shot Shaker was used to treat eleven hectares of lead shot-contaminated sediment within Wye Marsh during 1997 and 1998, and approximately 6 hectares of Hog Bay in 2001.

Since water level fluctuations and a number of other factors influence the number of cases of lead poisoning, it was not anticipated that remediation would completely eliminate lead poisoning in Trumpeter Swans and other waterfowl in Severn Sound, but it would reduce the availability of remnant lead shot in soft sediments and thus decrease losses resulting from ingestion of lead pellets in those areas.  The long neck of the Trumpeter swan enables them to reach depths in the sediment greater than most other waterfowl when foraging; this characteristic made them a practical choice for monitoring lead poisoning issues in Severn Sound.  Trumpeter Swans are useful as an indicator species: if few lead pellets are available to Trumpeter Swans foraging in wetland sediments, lead shot is also unavailable for most other waterfowl species.  Prior to remedial activity in 1997, as much as 20% of the free-flying Trumpeter swan population monitored by the Friends of Wye Marsh Inc. was affected by lead poisoning.  Remedial activity was initiated in 1997; following this, less than 10% of the population was affected, with the lowest recorded incidence occurring in 2000 (2.3%) and 2001 (4.3%).  Extensive testing of the prototype proved that the device was effective in sinking lead shot in soft wetland sediments, and the decreasing trend evident in the percentage of the free-flying population of Trumpeter Swans affected by lead poisoning prior to and after remediation of ‘hot spots’ in Severn Sound confirms this.

Environmental Effects

Biophysical Effects

Testing indicated that use of the Shot Shaker resulted in minimal effects to the surrounding aquatic environment.  Influence of remediation on the water column quality was short term, with conditions returning to near background conditions within a few hours of treatment.  Both water chemistry analyses and sediment analyses returned to typical control levels within 24 hours of remediation, and visible turbidity subsided within 2 hours. 

Biological Effects

Testing during the project indicated that invertebrate species were not seriously affected by the temporary disruption of the sediment profile caused by the operation of the vibration device. 

A number of mitigation measures were employed during the project, to further ensure minimal disruption to the surrounding aquatic environment:

<          Remediating areas prior to or following the active growing season to minimize disruption to vegetation.  The remedial activity may further act as a catalyst for growth by exposing dormant seeds.   

<          Appropriate timing of remedial activity to avoid interfering with breeding/spawning cycles of waterfowl, herptiles and fish.

<          Suitable timing of remediation to avoid interfering with waterfowl hunting season.

 Application limits

This technology will not be adequate to treat all wetlands contaminated with lead pellets.  It is designed to treat submerged silty sediments with densities that limit the natural sinking rate of lead pellets, and is recognized as having limited application in areas with hard clay surfaces or rock out-croppings.  Furthermore, the vibration device was designed for application in areas of high potential for lead shot accumulation (such as those near identified hunting sites/blinds), rather than broad-scale application in large wetlands.

References

Scheuhammer, A.M. and S.L. Norris.  1995. A review of the environmental impacts of lead shot shell ammunition and lead fishing weights in Canada . Canadian Wildlife Service Occasional paper Number 88.  Ottawa .

CWS (Canadian Wildlife Service).  1998.  Hinterland Who’s Who: Lead poisoning of water birds.  Environment Canada .  4 pp.