longer term. Thus, today, toxicity tests are carried out more and more at environmentally relevant concentrations focusing on physiological, biochemical, and
molecular endpoints. In this context, responses such as growth are evaluated under
increasing exposure conditions for the derivation of EC 50 values which can also be
used in traditional risk quotient approaches also considered in the EU TGD, by
applying a correspondently lower AF than to mortality data-derived LC 50 values.
In the case of biochemical and molecular responses, however, dose-response
curves are generally scarce, and derivation of a toxicity parameter is more complicated. Often, exposure experiments are carried out only at one or two environmentally relevant exposure concentrations to examine if a certain response occurs;
however, follow-up tests in a dose-response-dependent manner are generally
lacking, and a concrete value of the concentration affecting 50% of the individuals
is not derived. Thus, no toxicity parameter is available to perform practical risk
assessment in a traditional way employing the risk quotient approach. In this case, it
is important to define at what threshold concentration of the compound these
sublethal biochemical and molecular alterations translate into death or reproductive
failure affecting populations in the long term. Little research has attempted to
identify exposure thresholds at which observation of sublethal effects becomes a
practical predictor of toxicity, so far. To date, there is no established procedure for
risk evaluation relying on sublethal data, and scientists are still searching for a way to
incorporate these data in the risk evaluation process. Therefore, it is important to
characterize threshold responses to provide reasonable guidance for risk management measures. These sublethal alterations must not be underestimated, as aquatic
invertebrates are generally very sensitive components of aquatic ecosystems, and a
long-term exposure to bioactive compounds at low concentrations impairing basic
functions can reduce fitness and performance of the exposed organisms, with important consequences on population level. Evaluation of nonconventional sublethal
endpoints is imperative to assess the overall condition of the organism, and although
in some cases the exposed individual might be able to maintain homeostasis, in other
cases, especially when the stress persists, the organisms’ mechanisms may not be
effective enough to protect against the insult. Therefore, although sublethal endpoints
are often identified in toxicity tests, they are rarely used to inform future testing
decisions or to establish relevant exposure thresholds for complex substances, primarily due to the shortage of a standardized methodology [84].
5.1 Case Study: Sublethal Toxicity of DF and IB
in the Freshwater Shrimp Atyaephyra desmarestii
In order to assess the sublethal effects of exposure to the pharmaceuticals DF and IB,
Nieto et al. [19, 85] exposed the freshwater shrimp Atyaephyra desmarestii under
environmentally relevant exposure conditions.
Ibuprofen and Diclofenac: Effects on Freshwater and Marine Aquatic Organisms –. . .
175
molecular endpoints. In this context, responses such as growth are evaluated under
increasing exposure conditions for the derivation of EC 50 values which can also be
used in traditional risk quotient approaches also considered in the EU TGD, by
applying a correspondently lower AF than to mortality data-derived LC 50 values.
In the case of biochemical and molecular responses, however, dose-response
curves are generally scarce, and derivation of a toxicity parameter is more complicated. Often, exposure experiments are carried out only at one or two environmentally relevant exposure concentrations to examine if a certain response occurs;
however, follow-up tests in a dose-response-dependent manner are generally
lacking, and a concrete value of the concentration affecting 50% of the individuals
is not derived. Thus, no toxicity parameter is available to perform practical risk
assessment in a traditional way employing the risk quotient approach. In this case, it
is important to define at what threshold concentration of the compound these
sublethal biochemical and molecular alterations translate into death or reproductive
failure affecting populations in the long term. Little research has attempted to
identify exposure thresholds at which observation of sublethal effects becomes a
practical predictor of toxicity, so far. To date, there is no established procedure for
risk evaluation relying on sublethal data, and scientists are still searching for a way to
incorporate these data in the risk evaluation process. Therefore, it is important to
characterize threshold responses to provide reasonable guidance for risk management measures. These sublethal alterations must not be underestimated, as aquatic
invertebrates are generally very sensitive components of aquatic ecosystems, and a
long-term exposure to bioactive compounds at low concentrations impairing basic
functions can reduce fitness and performance of the exposed organisms, with important consequences on population level. Evaluation of nonconventional sublethal
endpoints is imperative to assess the overall condition of the organism, and although
in some cases the exposed individual might be able to maintain homeostasis, in other
cases, especially when the stress persists, the organisms’ mechanisms may not be
effective enough to protect against the insult. Therefore, although sublethal endpoints
are often identified in toxicity tests, they are rarely used to inform future testing
decisions or to establish relevant exposure thresholds for complex substances, primarily due to the shortage of a standardized methodology [84].
5.1 Case Study: Sublethal Toxicity of DF and IB
in the Freshwater Shrimp Atyaephyra desmarestii
In order to assess the sublethal effects of exposure to the pharmaceuticals DF and IB,
Nieto et al. [19, 85] exposed the freshwater shrimp Atyaephyra desmarestii under
environmentally relevant exposure conditions.
Ibuprofen and Diclofenac: Effects on Freshwater and Marine Aquatic Organisms –. . .
175