ENVIRONMENTAL QUALITY STANDARD REQUIREMENTS AND SYSTEM RECOVERY THROUGH PROBABILISTIC APPROACHES

12.4 ENVIRONMENTAL QUALITY STANDARD REQUIREMENTS AND SYSTEM RECOVERY THROUGH PROBABILISTIC APPROACHES

EQSs are concentration limits that should represent the theoretical ‘‘no effect’’ figure, and must be elaborated in European Union for a list of priority substances including pesticides to implement the WFD [135]. Often, published papers on pesticide monitoring state that determined residue levels have exceeded or not ‘‘safe’’ levels or that acute=chronic effect may be expected with reference to ‘‘maximum permissi- ble concentrations’’ (MPC) or ‘‘EQSs.’’

Since EQSs cannot be determined experimentally, some of the current procedures are based on the use of application factors to experimental NOECs [136]. However, SSDs have also been proposed to derive EQSs [137]. The extrapolation of using such

Monitoring of Pesticides in the Environment 349

TABLE 12.3 Methods for the Risk Assessment of Pesticides in the Environment Depending on the Data Availability and the Questions that Are Addressed in the Assessment

Method

Output Point estimate quotients

Exposure

Effects

A ratio of exposure –toxicity Distribution –point

Point estimation

Point estimation

Probability of exposure estimation comparison

Distribution

Point estimation

exceeding the effect levels Exposure and effect

Probability of certain effects distribution

Cumulative

Distribution

frequency occurring when a fixed comparison

distribution exposure level is exceeded Distribution-based

Probability distribution of quotients

Distribution (Monte

Distribution

Carlo simulation) quotients (probability that exposure exceeds toxicity)

Integrated exposure and Distribution (Monte

Probability and magnitude of effects distribution

Distribution

Carlo simulation)

(Monte Carlo

effect occurring

simulation)

TABLE 12.4 Tiered Risk Assessment Scheme

Risk Assessment Tier 1 (Deterministic)

Tier Level

Exposure Assessment

Screening level EEC based on a Is the EEC < point estimates of high-exposure scenario

toxicity for the most sensitive species (L(E)C 50 or NOEC) If yes ! no further assessment necessary; if no ! tier 2 or mitigate Tier 2 (Probabilistic)

Reasonable high-exposure EECs Is the upper 10th percentile of the based on improved model

distribution of EEC < the lower 10th simulations

percentile of the distribution of toxicity estimates (L(E)C 50 or NOEC) If yes ! no further assessment necessary; if no ! tier 3 or mitigate Tier 3

More specific scenarios for defining As for tier 2 geographical and climate-driven EECs

If yes ! no further assessment necessary; if no ! tier 4 or mitigate Tier 4

Site-specific EECs (pulsed exposures) As for tier 2 or use more realistic or landscape modeling confirmed

toxicity tests by environmental monitoring If yes ! no further assessment necessary; if no ! mitigate

Source: Modified from SETAC, Pesticide Risk and Mitigation, Final Report of the Aquatic Risk Assessment and Mitigation Dialog Group, SETAC Foundation for Environmental Education, Pensacola, FL, 220 pp., 1994.

350 Analysis of Pesticides in Food and Environmental Samples distributions for setting EQSs originated from past studies [110,130]. PNEC values

were calculated to serve as EQS by using the HC 5 values (hazardous concentration for 5% of species in the ecosystem under investigation) with a default safety factor of 5 as it is suggested in the EC Technical Guidance Document [108].

In addition, the need to develop quality objectives not only for single substances but also for mixtures of pesticides seems evident. For that purpose, the conceptual basis could be the use of the two existing biometric models: concentration addi- tion (CA) and independent action (IA) or response addition. They may allow calculation of the toxicity of mixtures of pesticides with similar modes of action (CA) and dissimilar modes of action (IA), respectively. The research project of Prediction and Assessment of the Aquatic Toxicity of Mixtures of Chemicals (PREDICT) [138] provided results for several multiple mixtures, composed of similarly as well as dissimilarly acting chemicals and revealed that significant mixture toxicity occurs even at a mixture concentration consisting of the sum of

the EC 01 concentrations of the mixture components. Thus, NOECs should not be generally considered as concentrations of no environmental concern with respect to multiple pesticide mixtures.

The rate of recovery of a system could also be estimated based on SSDs. The approach is based on the dissipation half-life of the pesticide (T 1=2 ), the initial concentration (C 0 ), and the hazardous concentration for 5% of species (HC 5 ) [139]. As an example, for the recovery of the system within a year after application, the pesticide’s half-life should meet the condition:

Although complete dissipation will be necessary for complete recovery, under some conditions it may not be sufficient and ecological recovery may lag behind the disappearance of the pesticide [124]. Of course, the factors that influence the recovery of biota population after a significant perturbation are complex and the earlier approach could be used only for preliminary assessment.