I composed this earlier and decided not to send it until I read Teresa
Michelsen's post today. I think I can add a little insight into the
behavior of one element, lead. Teresa's statements about the behavior of
metals in general show how difficult it is to predict the physiological and
ecological effects in the environment and how difficult it is to determine
appropriate remedial measures.

The subject of lead shot in sediment came up earlier, in mid-May. The
threat to waterbirds is real and the U.S. Fish and Wildlife Service has
gradually banned the use of lead shot throughout coastal areas starting in
1991 on the west coast. (Steel shot has been substituted but, since it is
one fourth the density of lead, leads to more crippling at longer ranges.
As a result barium, which is half as dense as lead and essentially
non-toxic, is being investigated for use as shot.) In aquatic systems,
throughout a broad range of pH values, elemental lead is insoluble. Under
anoxic conditions lead forms a sulfide which is moderately soluble under
acidic conditions, as occur in many marshes. In alkaline lakes lead can
form a hydroxide which is quite soluble. Soluble lead also can be taken up
by plants and transferred through the food web. As a result, screening
guidelines which establish a level of concern for toxicity are set in the
part per billion range for fresh and salt water, but in the parts per
thousand range for sediment. Most of the lead in the water column in Puget
Sound is particulate and ends up in the sediment where it is largely
unavailable to organisms. Lead shot is ingested by ducks and geese,
which are particle feeders. Lead fishing gear (mainly sinkers) are
ingested by loons and other fish eating birds. The low pH of gastric
fluids solubilizes the lead which enters the circulatory system and affects
the central nervous system.

Marshes and swamps, over which hunting has taken place for decades, have
accumulated large quantities of lead, in the grams per kg range; close to
lead ore!

Herb Curl
Seattle WA


h.curl at hazmat.noaa.gov "You may be only young once but you can be
Hazmat/NOAA, 7600 Sand Pt. Wy., NE immature the rest of your life."
Seattle, WA 98115-0070
(206) 526-6272