Linking in situ bioassays and population dinamics of macroinvertebrates to asses agricultural contamination in the streams of Argentine Pampa

S. JERGENTZ, ; P. PESSACQ,; H. MUGNI, C. BONETTO & R. SCHULTZ

ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY

Elsiever

Lugar: London; Año: 2004 vol. 59 p. 133 - 141

0147-6513

Bioassays with the genus Hyalella are used as a standard test to study the contamination of water and sediments in laboratory test in North America (EPA 2000). In this study the local species Hyalella curvispina was used to assess the contamination with insecticides under field conditions in two agricultural streams (Maguire and Horqueta) in the argentine Pampa. Together with the in situ bioassays the drift and the changes in abundance of the species in the streams were observed. The insecticides Chlorpyrifos, Cypermethrin and Endosulfan were during three runoff events in January and early Febuary. Chlorpyrifos was detected in the suspended sediment in a period of no rain (15 to 23.01.02) in Horqueta and spray drift is suggested as a way of introducing. In this period 100% mortality of Hyalella curvispina was observed in the in situ bioassay in Horqueta while in other periods with no rain the mortality was between 7 and 13% at the same site. Maguire showed a mortality of 75% in the same period but with no insecticide records while in the period before and after this rain event the mortality was between 10 and 11 %. Another in situ bioassay with the species Macrobrachium borrelli in the same period showed 100% mortality in Horqueta in contrast of 7% mortality of this species in Maguire. After a runoff event on the 5th of January, a drift peak with an average of 99 individuals per driftnet of Hyalella curvispina was observed in Horqueta. One week later the drift was still high (44 individuals/m2) with a lot of small (83%) individuals. The abundance of Hyalella curvispina in Horqueta was constant with an average of 106 and 103 individuals per square meter in the first (04.12.01) and the second (09.01.02) sampling. This number was reduced to zero in the third sampling (07.02.02) while in Maguire no significant changes in the abundance were observed. In between the second and the third sampling there were two runoff events with an introduction of insecticides and one introduction of Chlorpyrifos that may was caused by spray drift in Horqueta.