Multi-walled carbon nanotubes, natural organic matter, and the benthic diatom Nitzschia palea: "a sticky story".

Different effects of multi-walled carbon nanotubes (MWCNTs) on the freshwater diatom Nitzschia palea were examined. MWCNTs used in this study (MWCNT) were dispersed either by sonication without (MWCNT sonicated) or with a realistic concentration (10 mg L(-1)) of Natural Organic Matter (MWCNT+NOM). A pocket-size device was designed to distinguish shading effect (using MWCNT suspensions as external filters) from total exposure effect of MWCNT sonicated and MWCNT+NOM on benthic algae. This study demonstrates that cell division was strongly inhibited after a 48 h exposure to MWCNT+NOM compared to MWCNT sonicated. This device did not yield a quantifiable contribution of shading to growth inhibition of MWCNT sonicated and below 10 mg L(-1) of MWCNT+NOM. In all cases, neither lethal effects nor drops in photosynthetic quantum yield were observed. After a 6-d exposure, a complete growth recovery was observed for all conditions except at the highest concentration of MWCNT+NOM. Different microscopic approaches using carbohydrates markers revealed the strong affinity between MWCNT and extracellular polymeric substances (EPS) produced by N. palea. These seem to constitute a defensive mechanism against MWCNT.

Short term exposure to multi-walled carbon nanotubes induce oxidative stress and DNA damage in Xenopus laevis tadpoles.

The potential impact of Multiwalled Carbon NanoTubes (MWCNTs) was investigated on Xenopus laevis tadpoles exposed to 0.1, 1 and 10mg/L. Oxidative stress was measured in entire larvae exposed and DNA damage (Comet assay) was carried out in erythrocytes of circulating blood from 2h to 24h according to standardized recommendations. Results showed significant H2O2 production when larvae were exposed to 1mg/L and 10mg/L of MWCNTs after 4h and 2h of exposure, respectively. Antioxidant enzyme activities showed significant induction of catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD) from only 2h of exposure to 10mg/L of MWCNTs. In presence of 1mg/L of MWCNTs, only GR and CAT activities were significantly induced at 4h. Enzyme activities do not follow a simple dose-effect relation, but the time of induction is shortened in relation with the tested concentration. The Comet assay results showed significant DNA damages with a dose dependent response. The profiles of DNA damages show fluctuations, in course of time, which are characteristics of oxidative stress response in relation with the continuous balance between damage and compensation process.

1,4-dichlorobenzene marine risk assessment with special reference to the OSPARCOM region: North Sea.

This risk assessment on 1,4-dichlorobenzene was carried out for the marine environment, following methodology given in the EU risk assessment Regulation (1488/94) and Guidance Document of the EU New and Existing Substances Regulation (TGD, 1996). Data from analytical monitoring programs in large rivers and estuaries in the North Sea area were collected and evaluated on effects and environmental concentrations. Risk is indicated by the ratio of predicted environmental concentration (PEC) to predicted no-effect concentration (PNEC) for the marine aquatic environment. In total, 17 data for fish, 9 data for invertebrates and 7 data for algae were evaluated. Acute and chronic toxicity studies were taken into account and appropriate assessment factors used to define a final PNEC value of 20 microg/l. Recent monitoring data indicate that 1,4-dichlorobenzene levels in coastal waters and estuaries are below the determination limit of 0.1 microg/l used in monitoring programs. The worst case value recorded in river water is below 0.45 microg/l. Using these values, calculated PEC/PNEC ratios give safety margins of about 40-200, taking no account of dilution in the sea. Environmental fate and bioaccumulation data indicate that current use of 1,4-dichlorobenzene poses no risk to the aquatic environment.