Effects of chlorpyrifos in freshwater model ecosystems: the influence of experimental conditions on ecotoxicological thresholds

Abstract

Three experiments were conducted to determine the impact of the insecticide chlorpyrifos (single applications of 0.01 to 10 microg AI litre(-1)) in plankton-dominated nutrient-rich microcosms. The microcosms (water volume approximately 14 litres) were established in the laboratory under temperature, light regimes and nutrient levels that simulated cool 'temperate' and warm 'Mediterranean' environmental conditions. The fate of chlorpyrifos in the water column was monitored and the effects on zooplankton, phytoplankton and community metabolism were followed for 4 or 5 weeks. The mean half-life (t1/2) of chlorpyrifos in the water of the test systems was 45 h under 'temperate' conditions and about 30 h under 'Mediterranean' environmental conditions. Microcrustaceans (cladocerans and copepod nauplii) were amongst the most sensitive organisms. All three experiments yielded community NOEC (no observed effect concentrations) of 0.1 microg AI litre(-1), similar to those derived from more complex outdoor studies. Above this threshold level, responses and effect chains, and time spans for recovery, differed between the experiments. For example, algal blooms as an indirect effect from the impact of exposure on grazing organisms were only observed under the 'Mediterranean' experimental conditions. The relatively simple indoor test system seems to be sufficient to provide estimates of safe threshold levels for the acute insecticidal effects of low-persistence compounds such as chlorpyrifos. The robustness of the community NOEC indicates that this threshold level is likely to be representative for many freshwater systems.

Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States

“…Since the publication of the Giesy et al review, results of several cosm studies of CPY have featured prominently in comparisons of cosm studies, single-species laboratory toxicity tests, and regulatory benchmarks across classes of insecticides (Brock et al 2000(Brock et al , 2006Maltby et al 2005 ;van Wijngaarden et al 2005b ). Several newer cosm studies have broadened the scope of conclusions about chlorpyrifos effects on aquatic communities to a wider range of locations and environmental conditions (Daam et al 2008a , b ;López-Mancisidor et al 2008a , b ;van Wijngaarden et al 2005a ;Zafar et al 2011 ). The body of evidence from cosm studies is consistent in supporting the conclusion that concentrations of 0.1 μg CPY L −1 or less cause no ecologically signifi cant effects on aquatic communities.…”

“…Indoor, plankton-dominated microcosms were used to compare the responses of aquatic communities to CPY under conditions pertaining to Mediterranean regions (higher temperature and greater amounts of nutrients) with conditions representing cool temperate regions (van Wijngaarden et al 2005a ). CPY was applied once to give concentrations from 0.01 to 10 μg L −1 in water of microcosms.…”

Water pollution by agriculture

“…The effects can be measured in a general way and modelled with varying degrees of uncertainty (Johnes et al 1996;Van den Brink et al 2002;Bowes et al 2005;Westra et al 2005;Van Wijngarden et al 2005), but the sort of precision demanded by legislators and lobbies will never be attainable and this has been a major weapon used to delay regulation of agricultural activities.…”

Opinion of the Scientific Panel on Plant protection products and their residues (PPR) related to the aquatic risk assessment for cyprodinil and the use of a mesocosm study in particular

“…The number of zooplankton taxa observed in the cyprodinil mesocosm experiment (49 taxa) is in the upper end of the range of the number of zooplankton taxa observed in the various micro/mesocosm experiments performed (without fish) at Wageningen University and Research Centre (25 -50 taxa; see e.g. Van den Brink et al, 1996, andVan Wijngaarden et al, 2005a). In addition, the numbers of micro-crustacean taxa in the cyprodinil mesocosm study (13 taxa) fall within the range of the number of micro-crustacean taxa observed in these studies performed in Wageningen (11-20 taxa).…”