Effect of Prolonged Exposition to Pulp Mill Effluents on the Invasive Aquatic Plant Egeria Densa and Other Primary Producers: A Mesocosm Approach

Abstract

The recent disappearance of the aquatic plant Egeria densa, a Brazilian native invasive species, from a wetland in southern Chile prompted several efforts to unveil the origin of this phenomenon. Because these changes occurred by the time a newly built pulp mill started its operations in the area, a reasonable doubt for a cause-effect relationship is plausible. We implemented a mesocosm approach to directly evaluate the effect of treated pulp mill effluents (PMEs) on several growth-related parameters of E. densa as well as other primary producers. We hypothesize that effluent, at a dilution similar to that detected in the zone of the wetland where the negative environmental impacts were evident, has a significant negative effect on this aquatic plant as well as on other primary producers inside a mesocosm system. After a prolonged (months) exposure to both 0% PME with pure river water and a 4 to 5% (v/v) dilution of treated PME, no effect on E. densa was measured. Furthermore, plants exposed to effluent exhibited a significantly greater general growth rate. Coincidently, chlorophyll a concentration in the water column and periphyton biomass also changed over time, but without any pattern attributable to the effluent. Values of the autotrophic index obtained from the periphyton growth pattern did not suggest enrichment of the system with organic matter. Our results only refer to the direct effect of mill effluents on several biotic responses, but they represent an important advance toward generation of the scientific knowledge necessary to understand how the ecosystem functions while receiving this and other unquantified sources of water.

Do Subtoxic levels of chlorate influence the desiccation tolerance of Egeria densa?

“…Ever since the massive disappearance of E. densa from the wetland system during 2004, the suspicion that effluents from the Valdivia Paper Mill Plant were somehow responsible has been present [11], although this has never been proved, nor have the specific compounds within the effluents that could be toxic to E. densa been identified. In a previous study, Palma et al [14] exhibited experimental evidence, also using a mesocosm approach, that the treated effluents do not have a negative impact on E. densa, although no specific compounds were tested in their experiments. The suspicion that chlorate could be the specific agent capable of this massive negative impact is not new and probably has to do with the fact that chlorate is employed in agriculture as an herbicide and defoliating agent [3].…”

“…Plants of E. densa were kept for four weeks inside 10 1,000-L experimental tanks that received a continuous flow (2 L/min) of water from the Cruces River. The general experimental setup was similar to that used in another related study [14]. One-half of the tanks (treatment tanks) received an additional continuous amount of chlorate via a mechanical dispenser (Dosatron) inserted in the line that fed them.…”

“…Before being used in the experiment, a large number of plants collected in the nearby Calle-Calle River were acclimated for two weeks inside tanks with Cruces river water flowing through. Following a previously used methodology [14,15], only the top 30 cm (initial length) of the healthiest-looking plants were selected and considered for the experiment. Ten individually labeled plants were included inside each tank.…”

Monitoring of the Environmental Effects of Pulp Mill Discharges in Chilean Rivers: Lessons Learned and Challenges

“…Although no cause-effect relationships have been established, a series of scientifi c research publications pointed out several potential causes, such as natural changes (Marin et al 2009), the impact of heavy metals (Jaramillo 2005), and potential effects of ultraviolet radiation (Ramírez et al 2006). However, from a toxicological point of view, no specifi c chemical cause-effect relationships were established (Palma et al 2008). In this context, during the environmental impact assessment for that new mill in Chile, a monitoring program for dioxins and furans in the effl uent and the receiving environment was required by the regulatory agency (CONAMA).…”