Environmental Engineering Reference
In-Depth Information
are derived from incomplete data sets using methodology similar to those of
USEPA (1986), and are used only for implementation of narrative criteria.
4.2
Numeric Criteria of Different Types and Levels
Many existing criteria derivation methodologies include procedures for derivation
of more than one level or type of criterion for each toxicant (OECD 1995; ANZECC
and ARMCANZ 2000; La Point et al. 2003; RIVM 2001; Lepper 2002; USEPA
2003a). This refers either to (1) the derivation of different levels of criteria to meet
different regulatory goals, or (2) to the use of ecological risk assessment techniques
with increasing levels of technical sophistication, leading to criteria with site-specific
application and greater certainty (La Point et al. 2003). The second of these is
directly related to how much and what kinds of data are available for criteria derivation.
Note that derivation of separate acute and chronic criteria, as is done in the USEPA
(1985) and UK methodologies (Zabel and Cole 1999), is not what is meant here by
“different types and levels” of criteria.
Compartment-specific ERLs are derived in the Netherlands (RIVM 2001).
The three levels of ERLs are the ecosystem serious risk concentration (SRC ECO ), the
maximum permissible concentration (MPC), and the negligible concentration
(NC). The NC (concentration causing negligible effects to ecosystems) is calcu-
lated as the MPC divided by a safety factor of 100, and represents a regulatory
target value. The MPC is a concentration that should protect all species in ecosys-
tems from adverse effects. If concentrations in ambient waters are above the MPC,
discharges can be further regulated. Between the MPC and the NC, principles of
ALARA (as low as reasonably achievable) are used to continue reducing levels
toward the NC (Warmer and Van Dokkum 2002). The SRC ECO is a concentration at
which ecosystem functions will be seriously affected, or are threatened to be
negatively affected (assumed to be when 50% of species and/or 50% of microbial
and enzymatic processes are potentially affected; RIVM 2001). Waters exceed the
SRC ECO require cleanup intervention efforts.
In the French methodology (Lepper 2002), four threshold levels, corresponding to
biological quality and suitability classes for water bodies, are calculated for each
substance. Threshold level 1 indicates negligible risk for all species, and is derived
from either chronic or acute toxicity data, with safety factors applied. The level 2
threshold indicates possible risk of adverse effects for the most sensitive species, and
is derived from the same data as level 1, but smaller safety factors are applied. Levels
3 and 4 indicate probable or significant risk of adverse ecosystem effects, respec-
tively, and are derived solely from acute toxicity data. Tentative standards may be set
when a minimum data set is not available. Freshwater standards may be used as tentative
marine standards if insufficient marine data are available and there is no reason to
suspect greater sensitivity among marine species. None of the threshold values
derived by the French methodology are enforceable; the values serve as references
for assessments and development of action plans.
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