No abstract

Acute toxicity effects of sodium dodecyl sulfate (SDS), sodium pentachlorophenate (SPCP), and hexavalent chromium (Cr(VI)) were determined in Ceriodaphnia dubia, Daphnia pulex, and Simocephalus mixtus. Neonates were obtained from parthenogenetic females of different ages to establish the relative sensitivity of these species, in order to propose them as test organisms in the Mexican environmental standards. For C. dubia the average LC(50) (48 h) values were 8.59 +/- 1.08, 0.92 +/- 0.16, and 0.23 +/- 0.04; for D. pulex, 5.34 +/- 0.90, 1.49 +/- 0.29, and 0.28 +/- 0.06; whereas for S. mixtus, they were 4.50 +/- 0.41, 1.31 +/- 0.16, and 0.12 +/- 0.03 mg/L for SDS, SPCP, and Cr(VI), respectively. SDS and SPCP acute toxicity results depicted coefficients of variation of

Environmental standards for the regulation of drilling fluids used in petroleum facilities, land or offshore, do not exist in Mexican legislation, specially their toxicity limits. Thus, type and quality of these products and their toxicity are unknown, mainly those of oil constituents, which are highly toxic to aquatic biota and their early life cycles. In this study the LC50 (96 hours) of different drilling systems (generic fluids and field muds) using white shrimp ( Litopenaeus setiferus) in postlarvae stage were evaluated. This organism was selected because its regional distribution and economic importance. Also Mysidopsis bahia was used, only for comparing results, for assessing generic fluids because is applied as reference specie by USEPA. In order to know the white shrimp sensitivity, and its potential to be used as reference specie in Mexico, additional tests using Sodium dodecyl sulfate were run. A toxicity test procedure using L. setiferus is presented. Results with both species shown similar responses to generic fluids evaluations. Only one generic fluid was toxic for both species while the others did not. In case of field muds only two were toxic to L. setiferus because they were formulated with oil. It is recommended to include Litopenaeus setiferus postlarvae as a reference specie in Mexican Regulations for drilling fluids due to its distribution in Mexican petroleum offshore facilities and because of its replication and high sensitivity (similar to Mysidopsis bahia) in toxicity tests. Introduction Nowadays the Sonda of Campeche has been the scenery of very singular development for Mexico due to in this place have been joined two productive activities of different characteristics who represent an important foreign currency attraction for the country. First, the petroleum activity has permitted Mexico to be one of the most important petroleum producers in the world (1); second, the fishery activity, which for more than 20 years has represented a high fishing rate because of high diversity of aquatic environments related to the Sonda which are used for feeding and growing habitats of a great diversity of economic importance species as fishes and crustaceans. In the case of crustaceans, the shrimp fishing in Mexico represents the 60% of foreign currency obtained by marine products exportation (2) and Litopenaues setiferus or Gulf white shrimp is the more abundant specie in coastal Mexican zone of the Gulf of Mexico and also has higher relationship with estuarine environments (3); moreover, is an indicator specie of the interface water-sediment events. The aim of this study was to evaluate the potential of Litopenaeus setiferus as test specie for toxicological analysis of drilling fluids. To answer this, static acute toxicity tests (LC50-96 hours) were carried on with seven generic drilling fluids and six drilling muds used in offshore drilling facilities in the Sonda of Campeche area and with Sodium dodecyl sulfate as reference toxicant compound. For comparative purposes, the generic drilling fluids also were evaluated with Mysidopsis bahia, reference test specie used by United States Environment Protection Agency (USEPA). Materials and Methods Seven generic drilling fluids were used in toxicity tests and were prepared according with standard methods (4). After collecting from the return flow-line localized under the shale shaker, six field drilling muds also were tested: four were water-based (bentonitic, salty bentonitic, lignosulfonate inhibed and polimeric) and the other two were oil-based muds. For the water-based drilling muds, the tests were run in the suspended particle phase (SPP) following established procedure (5). The oil drilling muds were tested by placing in 1000 ml flask, 100 ml/900 ml (mud/marine water) by shaking (10 to 15 minutes) until mix was completed. The sample obtained was used as initial solution for preparing test concentrations.

In this study, native cladocerans, Scapholeberis armata freyi and Macrothrix elegans, were collected from the region and their offspring were used as test organisms to assess the effects of 18 corrosion and scale inhibitors, widely used to protect oil pipelines. Daphnia magna and Ceriodaphnia dubia were used as international reference species, and their sensitivity was compared to native species and assessed with the reference toxicant Cr(VI). We also determined the correlation between the native and the reference species. Corrosion inhibitors were grouped according to their uses and acute toxicity gradient; those used for multifunction pipelines are considered moderately toxic (LC(50) of 10 to 100 mg/L), and the remainder as toxic (LC(50) between 1.0 and 10 mg/L). Scale inhibitors are considered non-toxic, since the LC(50) for the 4 species exceeded 2,000 mg/L. Sensitivity test to Cr(VI) indicated that M. elegans was the least sensitive species. There was a high correlation (> 90%) in sensitivity among M. elegans, D. magna, and C. dubia to the corrosion inhibitors used. Hence, it is feasible to use these native species from Southeast Mexico as substitutes of the typical reference species.