Ambient Toxicity Monitoring Program

Regional staff recommend quarterly collection of ambient water and biannual collection of sediment for a minimum of one year, in conjunction with other chemical and biological monitoring. Continued monitoring is recommended for waterbodies that exhibit toxic effects. The database also includes the results of one-time collections made during intensive surveys or special studies.

Grab samples of ambient water are collected on a single day, in sufficient volume to provide for renewal during the tests. This approach is inconsistent with guidance (U.S. EPA 1994), developed primarily for regulatory application, which suggests daily sampling or a minimum of three samples collected every other day. The decision to collect a single sample for testing is based on consideration of personnel and travel costs for renewal sample collection. Samples are generally collected during other ambient monitoring and require no additional travel.

It should also be noted that the Pimephales promelas embryo-larval survival and teratogenicity test routinely used in the ambient toxicity monitoring program differs from the larval survival and growth test required of National Pollutant Discharge Elimination System (NPDES) permittees. The embryo-larval test was selected as a more cost-effective initial screening test. (Pickering 1988) suggests that the two tests offer similar repeatability, although the sensitivity of the tests may vary with different toxicants. When a NPDES permittee is suspected as a source of toxicity, the larval survival and growth test may be requested by participating agencies. Also, investigators should consider making return trips to the site(s) to collect samples for renewal of test water for consistency with NPDES permit test requirements.

Water samples are collected from the main flow of the stream in a clean polyethylene container(s) rinsed with ambient water before filling. Sediment samples are composited from a minimum of three subsamples of the upper layer of recently deposited, unconsolidated sediment. Subsamples are composited and mixed before being transferred to a clean glass or polyethylene container(s). Collecting equipment is thoroughly cleaned between sites and rinsed with ambient water before use. Upon collection, water and sediment samples are placed in ice for shipment to the laboratory.

In the laboratory, basic water chemistry tests are conducted on water and sediment elutriates to identify factors that may contribute to toxic effects. These tests include pH, alkalinity, hardness, conductivity, total residual chlorine, total ammonia-N, and unionized ammonia-N (determined only when total ammonia-N is elevated).

Sediment elutriates are prepared by combining a subsample from the homogenized sediment sample with appropriate culture water. The sediment and water are combined in a sediment-to-water ratio of 1:4 by volumetric displacement. After combining, the mixture is tumbled end-over-end for approximately 24 hours, after which the mixture is allowed to settle for an additional 24 hours at 3 - 4 ° C. After settling, the elutriate is siphoned off and filtered through a 1.5 micron glass fiber filter. Standard laboratory tests and statistical data analyses are conducted according to Short-term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms (U.S. EPA 1994), Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Marine and Estuarine Organisms ( U.S. EPA 1994), and Methods for Measuring the Acute Toxicity of Effluents to Freshwater and Marine Organisms (U.S. EPA 1993) (Table 1.)

Ceriodaphnia dubia seven-day survival and reproduction; short-term chronic test observing mortality and number of offspring per female.

Daphnia pulex 48-hour survival; acute test observing mortality rate (no longer used for ambient testing program).

Pimephales promelas (Fathead Minnow) seven-day embryo-larval survival and teratogenicity; short-term chronic test observing mortality rate, teratogenic effects, and/or abnormal swimming behavior.

Pimephales promelas (Fathead Minnow) seven-day larval survival and growth; short-term chronic test observing mortality rate and dry weight at test termination (used for consistency with NPDES permit testing requirements).

Cyprinodon variegatus (Sheepshead Minnow) nine-day embryo-larval survival and teratogenicity; short-term chronic test observing mortality rate, teratogenic effects, and/or abnormal swimming behavior (used for estuarine or saline waters).

Selenastrum capricornutum 96-hr growth test; short-term test observing growth stimulation or inhibition (no longer used).

Because the primary objective of the program is to identify waterbodies that may be affected by toxicity, "toxic effects" include any any test endpoint (Table 1) that differs significantly from the endpoint observed in a laboratory control. Ambient water samples are analyzed without dilution, based on the assumption that this approach best represents instream conditions.