Monitoring of organochlorine and organophosphorus pesticides in the water of the Reconquista River (Buenos Aires, Argentina).

The Reconquista river is a typical example of the adverse impact of human activity on a watercourse. Approximately 10% of the population of the country is settled on its basin and it receives wastewater discharges from residences and industries. This paper describes the results of the first systematic data for measurement of pesticides in surface water of the river, based on a monthly monitoring program over two-year span. The analyses were performed, in three sampling stations (S1, S2 and S3), along 46 km of its course, following the AOAC methods. Screening included the following pesticides: (a) Organochlorines: alpha, beta and gamma HCH; heptachlor, heptachlor epoxide; aldrin; endrin; dieldrin; op' and pp' DDT; op' and pp' DDE; alpha and gamma chlordane and endosulphan II; (b) Organophosphates: ethyl and methyl parathion; chlorpyrifos and fenitrothion. From the 60 samples analyzed, 35% contained organochlorine pesticides in a concentration higher than the detection limit. Organophosphates were found in no case. Throughout the studied period, DDT and its metabolite DDE were only found in S1 and gamma chlordane in S3; heptachlor was present in 50% of the samples of S2 and in 35% of S3, while HCH isomers were detected in 38% of S2 and 45% of S3 samples. Neither temporal nor spatial trends were found. There was not a relationship between the time of samplings and the fumigation season for farming purposes. At all locations, pesticides levels were found to be between 40 and 400 times higher than the legal limits established for protection of aquatic life.

Effects of zinc on the structure and growth dynamics of a natural freshwater phytoplankton assemblage reared in the laboratory.

The response of a natural phytoplankton assemblage to different concentrations of Zn(2+) was evaluated by means of a static laboratory bioassay. Aliquots of surface water, taken in autumn from a non-polluted point of the Reconquista River (Buenos Aires, Argentia), were incubated in mineral nutrient media containing 2.5, 10 or 25 mg litre(-1) of Zn(2+) (as zinc chloride). The comparative structure and dynamics of the communities were followed through periodic physico-chemical and biological analyses of samples taken during 24 days of incubation. Under the experimental conditions of the bioassays, the existence of several Zn(2+) tolerant algal species was shown: the most important of them were Chlorella vulgaris Beij. (Chlorophyceae, Chlorococcales), Nitzschia palea (Kütz.) Smith and Gomphonema parvulum (Kütz.) Kütz. (Bacillariophyceae). It was also demonstrated that the algal responses to Zn(2+) were selectively concentration dependent: at 2.5 and 10 mg litre(-1) a stimulatory effect was observed in the diatoms; at 25 mg litre(-1), diatom toxicity occurred. In contrast, Chlorophyceae growth was stimulated at the maximal Zn level. In general, the diversity, richness and equitability of the community were adversely affected by Zn in a concentration-dependent fashion.

Impacto del Zn sobre microalgas dulceacuicolas del rio Reconquista (Buenos Aires) ; bioensayo multiespecifico de invierno

Se diseñó un bioensayo multiespecífico estático de laboratorio a fin de evaluar la respuesta de una comunidad algal de invierno a diferentes concentraciones de zinc. (2,5; 10,20 y 45 mg.1-1). Su efecto fue concentracion-dependiente, estimulacion del crecimiento hasta 10 mg.1-1 y signos de toxicidad a 20-45 mg.1-1. Se registraron especies tolerantes en las condiciones del bioensayo: Chlorella vulgaris, Nitzschia palea, Synedra ulna var. amphirrynchus y Gomphonema parvulum

Impacto del Zn sobre microalgas dulceacuicolas del rio Reconquista (Buenos Aires) ; bioensayo multiespecifico de invierno

Se diseñó un bioensayo multiespecífico estático de laboratorio a fin de evaluar la respuesta de una comunidad algal de invierno a diferentes concentraciones de zinc. (2,5; 10,20 y 45 mg.1-1). Su efecto fue concentracion-dependiente, estimulacion del crecimiento hasta 10 mg.1-1 y signos de toxicidad a 20-45 mg.1-1. Se registraron especies tolerantes en las condiciones del bioensayo: Chlorella vulgaris, Nitzschia palea, Synedra ulna var. amphirrynchus y Gomphonema parvulum