The Risk Evaluation Framework (REF), developed by Environment Canada, is applied to chemical substances in order to determine whether or not an environmental emergency (E2) plan should be required. For those substances that are evaluated as requiring an E2 plan, the next step is to determine a threshold quantity for the total quantity of the substance and the maximum storage container size on site. Within the REF, three categories are used to evaluate chemicals and assign threshold quantities. Shown below are the details within the three categories for arsenic acid:
|Value||Vapour Cloud Explosion (Yes/No)||Combustible (Yes/No)||References|
|Boiling point (°C)||160||No||No||(ATSDR, 2000; Lewis, 2001; Genium, 2004)|
|Flash Point (°C)||Non-combustible solid||(Genium, 2004; ATSDR, 2000)|
The data from the above mentioned categories were used to determine the various environmental/human thresholds. The threshold quantities relate to: carcinogenicity, aquatic toxicity, inhalation toxicity, vapour cloud explosion, combustibility, and reactivity.
The threshold quantity for carcinogenicity is defaulted to 0.22 tonnes, if it meets the following criteria:
1) have an IARC rating of 1, 2A or 2B, or have a US EPA rating of A, B1, or B2;
2) be persistent in any media for greater than 5 years.
Threshold quantities assigned as a result of aquatic toxicity are based on the following table:
|Criteria||Extremely Toxic||Highly Toxic||Moderately Toxic||Slightly Toxic|
|Persistence (water)||≥ 6 months||≥ 2 months to < 6 months||N/A||N/A|
|Bioaccumulation||BCF ≥ 5000 or Log Kow ≥ 5||BCF ≥ 500 to < 5000 or Log Kow ≥ 4 to < 5 (unless BCF < 500)||N/A||N/A|
|Acute Aquatic Toxicity (96 hrs LC50 – mg/L)||≤ 0.1||> 0.1 to ≤ 1||> 1 to ≤ 10||> 10 to ≤ 100|
|Threshold Quantity Tonnes (lbs)||0.22 (500 lbs)||1.13 (2 500 lbs)||4.50 (10 000 lbs)||9.10 (20 000 lbs)|
A substance is a candidate for a vapour cloud explosion if its flash point is < 23°C and its boiling point is < 35°C . A substance is considered combustible if its flash point is < 23°C or its boiling point is < 35°C . In accordance with the precautionary principle, the category with the lowest threshold will be used. For further explanation, please refer to the Implementation Guidelines for Part 8 of the Canadian Environmental Protection Act, 1999 – Environmental Emergency Plans. (http://www.ec.gc.ca/ee-ue/)
For arsenic acid # 28, the E2 hazard threshold was triggered by:
1) Aquatic toxicity at 0.22 tonnes;
2) Carcinogenicity at 0.22 tonnes.
Therefore, arsenic acid # 28 is recommended for addition to Schedule 1 of the Environmental Emergency Regulations under Part 3 with a threshold quantity of 0.22 tonnes.
ATSDR (Agency of Toxic Substances and Disease Registry). Toxicological Profiles for Arsenic. Centre for Disease Control. PB/2000/108021. 2000. p. 232. World Wide Web accessed October 2004.
Dyer, S.D., G.L. Brooks, K.L. Dickson, B.M. Sanders, and E.G. Zimmerman. “Synthesis and Accumulation of Stress Proteins in Tissues of Arsenite-Exposed Fathead Minnows (Pimephales promelas).” 1993. Environ.Toxicol.Chem. 12: 913-924.
Genium. “Material Safety Data Sheet – Arsenic Acid.” Release 58. CD-ROM. Genium Publishing Corp. Schenectady, NY. 2004.
HSDB (Hazardous Substances Data Bank). Arsenic, elemental. Canadian Centre for Occupational Health and Safety. U.S. National Library of Medicine. 2004. World Wide Web accessed October 2004.
IARC (International Agency for Research on Cancer). Arsenic and Arsenic Compounds. 1987. World wide web accessed October 2004.
Lewis Sr., R.J., Hawley's Condensed Chemical Dictionary. 14th Edition. John Wiley & Sons Inc. New York. 2001. p. 92.
Mackay, D., E. Webster, D. Woodfine, T.M. Cahill, P. Doyle, Y. Couillard, and D. Gutzman. “Contributed Articles Towards Consistent Evaluation of the Persistence of Organic, Inorganic and Metallic Substances”. 2003. ASP. Canadian Environmental Modelling Centre and Environment Canada. Human and Ecological Risk Assessment 9: 1445-1474. ISSN: 1080-7039.
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