{"id":681,"date":"2010-06-14T21:05:27","date_gmt":"2010-06-15T02:05:27","guid":{"rendered":"http:\/\/blogs.edf.org\/nanotechnology\/?p=681"},"modified":"2024-02-12T11:00:59","modified_gmt":"2024-02-12T16:00:59","slug":"epa-data-show-dispersants-plus-oil-are-more-toxic-than-either-alone","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/health\/2010\/06\/14\/epa-data-show-dispersants-plus-oil-are-more-toxic-than-either-alone\/","title":{"rendered":"EPA data show dispersants plus oil are more toxic than either alone"},"content":{"rendered":"

Richard Denison, Ph.D.<\/em>, is a Senior Scientist.<\/em><\/p>\n

In an earlier post<\/a>, I noted in haste some apparent discrepancies between EPA and BP acute toxicity data on the Corexit\u00ae dispersants.\u00a0 Little did I realize that the data mixup was actually telling me something much more significant:\u00a0 that the dispersant maker\u2019s own test data demonstrate that the combination of oil plus<\/em> dispersant is quite a bit more toxic than the dispersant alone and \u2013 even more significant \u2013 the combination is more acutely toxic than the oil by itself.<\/p>\n

Let me repeat that:\u00a0 The data indicate that dispersed oil is more toxic than undispersed oil.\u00a0 EPA has posted the dispersant manufacturer Nalco\u2019s \u201cTechnical Product Bulletins\u201d for each of the dispersants that have been used in the Gulf:\u00a0 Corexit\u00ae EC9527A<\/a> and Corexit\u00ae EC9500A<\/a>.<\/p>\n

Section VII of each of the bulletins shows the toxicity data for a) dispersant alone, b) the reference oil used in the test, No. 2 fuel oil, and c) a mixture of dispersant and test oil at a 1:10 ratio.\u00a0 Here are the data (remember, the lower the value, the more toxic the substance):<\/p>\n\n\n\n\n\n\n\n\n\n\n\n
\u00a0<\/strong><\/td>\n\u00a0<\/strong><\/td>\nLC50* values in parts per million (ppm)<\/strong><\/td>\n<\/tr>\n
\u00a0<\/strong><\/td>\n\u00a0<\/strong><\/td>\nMenidia (inland silverside fish)
\n96-hour test<\/strong><\/td>\n		Mysidopsis
\n(mysid shrimp)
\n48-hour test<\/strong><\/td>\n<\/tr>\n
Corexit<\/strong>\u00ae<\/strong> EC9500A<\/strong><\/td>\nDispersant alone<\/td>\n25.20<\/td>\n14.57<\/td>\n<\/tr>\n
No. 2 fuel oil alone<\/td>\n10.72<\/td>\n16.12<\/td>\n<\/tr>\n
Dispersant : oil
\n(1 : 10)<\/td>\n		2.61<\/td>\n3.40<\/td>\n<\/tr>\n
Corexit<\/strong>\u00ae<\/strong> EC9527A<\/strong><\/td>\nDispersant alone<\/td>\n32.23<\/td>\n24.14<\/td>\n<\/tr>\n
No. 2 fuel oil alone<\/td>\n10.72<\/td>\n16.12<\/td>\n<\/tr>\n
Dispersant : oil
\n(1 : 10)<\/td>\n		4.49<\/td>\n6.60<\/td>\n<\/tr>\n
*LC50 = concentration at which 50% of the test organisms are killed within the duration of the test.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

To put these numbers in perspective, consider this calculation (thanks to Sayer Ji at Gulf Oil Spill Truth<\/a> for starting me down this path of calculations):<\/p>\n

Just 2.61 parts per million of a 1:10 mixture of Corexit\u00ae EC9500A and oil kills 50% of silverside fish within 96 hours, at least under the test conditions.<\/p>\n