chloromethane; methyl chloride

Endpoint summary

Additional information

Aquatic toxicity data on fish, algae and plants are available for chloromethane but as chloromethane is a volatile substance, closed systems are required to maintain stable test concentrations. Alternatively, exposure concentrations can be verified using analytical measurements. It is unclear from the description of the studies if vessels were closed or not, and because all results are based on nominal concentrations the results should be evaluated with caution, except for the Daphnia magna study from DOW (2002). The Daphnia magna study was conducted under static-renewal test conditions (renewel at 24h) in a closed (no headspace) system and analysis of exposure solutions following 24 hours of aging in closed vessels without headspace showed little to no loss of test substance.

Chloromethane can be considered as a chemical which acts by narcotic toxicity, based on the classification system developed and validated by Verhaar et al. (1992; 2000). It is a chemical containing carbon, hydrogen and a halogen. This implies that the effects in the aquatic environment of chloromethane can be well described by QSARs for so-called Narcosis Class I type compounds (Verhaar et al, 1992). This QSAR uses the octanol-water partitioning constant Kow as a descriptor to assess the toxicity. For chloromethane, calculated log Kow values of 0.9-1.09 have been published (Eurochlor, 2006). Calculations were carried out using log Kow of 0.91 for chloromethane giving the highest estimated toxicity (SIDS, 2002).All data - experimental as well as QSAR estimates - give comparable results for fish, daphnia and aquatic plants. They indicate a relatively low toxicity. Therefore, it is justified to derive a PNEC based on the most sensitive short term study withDaphnia magna, revealing the most sensitive reliable result using an assessment factor of 1000:

 LC50 (48h) = 200 mg/L Daphnia magna.

The amount of chloromethane introduced into the environment must be seen in the context of the background input due to natural sources and the available data on aquatic organisms show toxicities of chloromethane far in excess of natural occurring concentrations. Backround concentrations of chloromethane is available, most of them in the. One European study was found (Hendriks & Stouten, 1993), a maximum concentration of 12μg/L in the riverwas reported (CIDCAD 28, 2000).Actual monitoring data (2010) from different productions sites inreveal concentrations of 3 µg/L and < 10 µg/L in the effluents of sewage treatment plants.Two ranges of (marine) aquatic exposure concentrations are given in the literature. These are in good agreement. The ranges are 3 to 5 ng/L for ocean water samples (Moore et al., 1996) and concentrations in sea water reported by Harper (2000) were 5 ng/L, with a range of 4-6 ng/L (EuroChlor, 2006).

Furthermore, as high production volume substances chloromethane have been reviewed to a great extant for their exposure potential to the environment and the possible risks arising from the substance (BUA 1986, OECD SIDS 2002, CICAD 2000 and Euro Chlor 2006,Environment Canada, 2009). It was concluded that chloromethane is currently of low priority for further work because of its low hazard profile.