Methods for Deriving Pesticide Aquatic Life Criteria - Reviews of Environmental Contamination and Toxicology - page 63

happen in the Sacramento and San Joaquin River basins, where short-term toxicant
pulses, coincident with pesticide use or storm events, occur regularly (Bailey et al. 2000;
Dileanis et al. 2002, 2003; Domagalski 2000; Dubrovsky et al. 1998; Kratzer et al.
2002; Kuivila et al. 1999; Werner et al. 2000). Many single-species studies have
shown that pulse exposures to toxicants can cause significant effects in aquatic
organisms that may induce population-level effects (Schulz and Liess 2000; Brown
et al. 2002; Ingersoll and Winner 1982; Forbes and Cold 2005; Cold and Forbes
2004; Hodson et al. 1983). However, in mesocosm studies, or in population-level
analysis of single-species tests of pulsed pesticide exposures, no long-term effects
were found (Heckman and Friberg 2005; Reynaldi and Liess 2005; Pusey et al.
1994). In the latter studies, some period of recovery was required (as rapid or 2-3
week). Presumably, if a community were to receive another pulse exposure before
full recovery, effects of the new pulse would be superimposed on those of the first.
Thus, it is important to have water quality criteria that are defined in terms of
magnitude, duration and frequency, in such a way that monitoring programs can be
readily designed to determine exceedances.Two basic approaches are used to
address exposure in existing criteria derivation methodologies. First, is to incorporate
some combination of magnitude, duration and frequency, in each criterion
statement (USEPA 1985; Zabel and Cole 1999; Roux et al. 1996). Second, is to
derive only exposure magnitude, and leave decisions on duration and frequency
to site-specific management (ANZECC and ARMCANZ 2000; CCME 1999;
Lepper 2002; BMU 2001; Irmer et al. 1995; OECD 1995; RIVM 2001; ECB 2003;
Bro-Rasmussen et al. 1994; Samsoe-Petersen and Pedersen 1995).
The USEPA criteria (1985) are expressed in terms of magnitude, duration and
frequency, with separate acute and chronic criteria. Magnitude is determined by
analysis of effects data, but duration and frequency are the same for all toxicants.
The allowable exposure durations, expressed as an averaging period of 4 d for
chronic toxicity, and 1 hr for acute toxicity, are meant to restrict concentration
fluctuations above the criteria in receiving waters. As mentioned, several studies
have shown that pulses of high exposure can cause greater effects in single-species
toxicity tests, than the same average constant concentration. It follows that mini-
mizing the length of the averaging period will minimize concentration fluctua-
tions during the period. When the USEPA criteria guidelines were developed, there
were few studies to support the notion that observed chronic toxicity resulted from
toxicant effects on a sensitive life stage over a relatively short period. However,
recent USEPA toxicity test guidance (USEPA 2002b) indicates that chronic toxic-
ity may be estimated by sensitive life-stage tests lasting 4-7 d, in lieu of full life-
cycle tests. Thus, for chronic toxicity, the 4 d averaging period seems reasonable. Four
d is long enough to observe the equivalent of chronic toxicity, but minimizes oppor-
tunities for concentration fluctuations.
The 1 hr period for acute toxicity is somewhat arbitrary and is based on (1) the
fact that it is shorter than the period of a typical acute test; and (2) a nonreferenced
opinion that “high concentrations of some materials can cause death in one to three
hr” (USEPA 1985). The Technical Support Document for Water Quality-based
Toxics Control (TSD; USEPA 1991) indicates that the 1 hr period is derived from