Assessing the effects of pulsed waterborne copper toxicity on life-stage tilapia populations

A modelling framework to assess multiple metals impacts on marine food webs: Relevance for assessing the ecological implications of deep-sea mining based on a systematic review

Industrial deep-sea mining will release plumes containing metals that may disperse over long distances; however, there is no general understanding of metal effects on marine ecosystems. Thus, we conducted a systematic review in search of models of metal effects on aquatic biota with the future perspective to support Environmental Risk Assessment (ERA) of deep-sea mining. According to results, the use of models to study metal effects is strongly biased towards freshwater species (83% freshwater versus 14% marine); Cu, Hg, Al, Ni, Pb, Cd and Zn are the best-studied metals, and most studies target few species rather than entire food webs. We argue that these limitations restrain ERA on marine ecosystems. To overcome this gap of knowledge, we suggest future research directions and propose a modelling framework to predict the effects of metals on marine food webs, which in our view is relevant for ERA of deep-sea mining.

Investigation on Immune-Related Protein (Heat Shock Proteins and Metallothionein) Gene Expression Changes and Liver Histopathology in Cadmium-Stressed Fish

Heat shock proteins (HSP) are highly conserved in their structure and released in case of stress. Increased metallothionein (MT) synthesis is associated with increased capacity for binding heavy metals. Healthy juveniles of grass carp were exposed to sublethal dose (1.495 mg L⁻¹) of cadmium for 28 days. Simultaneously, a control group was also run to compare difference of total RNA expression levels in cadmium-treated and control groups. The cadmium levels in the tissues of treated fish recorded were 1.78 ± 0.10 mg L⁻¹, 1.60 ± 0.04 mg L⁻¹, and 2.00 ± 0.05 mg L⁻¹, respectively. Several histological alterations including edema, hemorrhage, dilated sinusoids, hypertrophy, hyperplasia, congestion of central vein, and nuclear alterations were observed in cadmium-exposed fish. Stress gene (metallothionein and heat shock proteins) mRNA transcription levels were studied by mRNA extraction and cDNA preparation by using PCR. The expression level of heat shock protein gene was higher as compared to metallothionein and beta-2-microglobulin gene after cadmium exposure. This study reports various stress-related immune-responsive changes of immune proteins, heat shock proteins, metallothionein, and histopathological changes in fish due to cadmium toxicity that make the fish immunocompromised which may be considered as the biomarkers of cadmium toxicity in other experimental species.

Generational sensitivity alteration in Chironomus yoshimatsui to carbamate and pharmaceutical chemicals and the effect on Catalase, CYP450, and hemoglobin gene transcription

To ascertain the tolerance mechanisms of aquatic organisms to artificial chemicals, intergenerational sensitivity changes of Chironomus yoshimatsui to a carbamate pesticide (pirimicarb) and pharmaceutical chemical (diazepam) were investigated. The larvae (<48-h-old) in each generation were exposed to both chemicals for 48 h and then the surviving chironomids were cultured until the fifth generation (F0-F4) without chemical addition. The 48-h 50% effective concentration (EC₅₀) value of chironomids was determined for each generation. In the pirimicarb treatment group, the EC₅₀ values significantly increased in F3 and F4, and those in the diazepam treatment group slightly increased. Catalase, Cytochrome P450 and hemoglobin (Hb) mRNA levels were monitored to see whether these were related to the trans-generational sensitivity. Although the generalized linear model results showed that the sensitivity to diazepam was slightly increased in the diazepam treatment, we could not find any mRNA levels related to sensitivity alteration. In contrast, the model approach showed that the chironomids exposed to pirimicarb trans-generationally became tolerant with increasing Hb mRNA levels. Therefore, they might decrease their chemical stress by modifying Hb gene transcription.

Effects of Vegetation Restoration on Soil Enzyme Activity in Copper and Coal Mining Areas

Mining areas are suffering from serious environmental hazards, such as soil erosion, water pollution as well as land degradation. In this study, two types of mining areas in Anhui Province, China-one a copper mining area and the other a coal mining area-were selected to compare the soil properties under different vegetation restoration conditions, which can be generally classified into reclaimed and non-reclaimed areas. Soil catalase and urease activities and soil chemical properties were chosen to be the main indicators of soil quality. Principal component analysis was used to evaluate the overall soil fertility in the copper and coal mining areas. Results showed that in the copper mining area soil catalase activity was between 12.36 and 19.17 μg g^-1 h^-1 and urease activity was between 0.03 and 12.05 μg g^-1 h^-1. And in coal mining area, soil catalase activity was between 3.52 and 9.72 μg g^-1 h^-1 and urease activity was between 2.71 and 10.81 μg g^-1 h^-1. Moreover, soil catalase and urease activities in degraded areas were lower than those in reclaimed areas. Soil catalase activity and soil urease activity were significantly correlated with total potassium and total nitrogen, respectively. Soil quality in land types with vegetation restoration was higher than in non-reclaimed areas and old subsidence areas, while soil quality in the copper mining area was generally higher than in the coal mining area. Thus, the optimum measure in this region to ameliorate these degraded soils is vegetation restoration, which helps not only to improve the environment, but also to enhance soil quality in these degraded lands.

Influence of Hardness and Dissolved Organic Carbon on the Acute Toxicity of Copper to Zebrafish (Danio rerio) at Different Life Stages

Copper (Cu) bioavailability varies under water conditions. In the present study, the whole life of zebrafish was divided into three different life stages (larvae, juvenile and adult) based on the growth curve, then the influences of water hardness and dissolved organic carbon (DOC) concentration on the acute toxicity of zebrafish were respectively investigated. The results indicated that the life stages had significant effects on Cu toxicity. The larvae stage was less sensitive to Cu than both the juvenile and adult stages. With the increase of water hardness, the toxicity of Cu on zebrafish was decreased, a linear relationship was observed between water hardness and Cu toxicity, and the same was true for DOC concentration. The results showed that taking the 24 days juvenile zebrafish to study the water quality criteria of Cu was stable, sensitive and economical.

Impacts of suspended sediment and metal pollution from mining activities on riverine fish population-a review

Mining activities are responsible for the elevated input levels of suspended sediment and hazardous metals into the riverine ecosystem. These have been shown to threaten the riverine fish populations and can even lead to localized population extinction. To date, research on the effects of mining activities on fish has been focused within metal contamination and bioaccumulation and its threat to human consumption, neglecting the effects of suspended sediment. This paper reviews the effects of suspended sediment and metal pollution on riverine ecosystem and fish population by examining the possibilities of genetic changes and population extinction. In addition, possible assessments and studies of the riverine fish population are discussed to cope with the risks from mining activities and fish population declines.

The use of time-averaged concentrations of metals to predict the toxicity of pulsed complex effluent exposures to a freshwater alga

Intermittent, fluctuating and pulsed contaminant discharges may result in organisms receiving highly variable toxicant exposures. This study investigated the toxicity of continuous and pulsed exposures of a complex, neutralised drainage water (NDW) and dissolved copper-spiked dilute NDW to the green alga, Pseudokirchneriella subcapitata. The effects of single pulses of between 1 and 48 h duration and continuous exposures (72 h) on algal growth rate inhibition were compared on a time-averaged concentration (TAC) basis. Algal growth rates generally recovered to control levels within 24-48 h of the pulse removal. Continuous exposures to NDW resulted in similar or marginally higher toxicity to the algae when compared to pulsed exposures of equivalent TAC (% NDW). The toxicity of the NDW was attributed mostly to the metals, with the major cations potentially causing effects that are both additive (direct toxicity) and antagonistic (lower bioavailability of trace metals). For dissolved copper in dilute NDW, the pulsed exposures caused slightly higher toxicity than continuous exposures of equivalent dissolved copper TAC, with much of the difference explained by differences in labile copper concentrations between treatments. The results indicate that water quality guideline values for toxicants derived from continuous chronic exposures may be relaxed for pulsed exposures by a factor related to the TAC with the intent to provide an adequately protective but not overly-conservative outcome. The study highlights the influence that natural water quality parameters such as water hardness and DOC can have metal speciation and toxicity, and indicates that these parameters are particularly important for site-specific water quality guideline value derivation where, on a TAC basis, pulsed exposures may be more toxic than continuous exposures typically used in guideline value derivation.

Time-averaged concentrations are effective for predicting chronic toxicity of varying copper pulse exposures for two freshwater green algae species

Intermittent, fluctuating and pulsed contaminant discharges may result in organisms receiving highly variable contaminant exposures. This study investigated the effects of dissolved copper pulse concentration and exposure duration on the toxicity to two freshwater green algae species. The effects of single copper pulses of between 1 and 48 h duration and continuous exposures (72 h) on growth rate inhibition of Pseudokirchneriella subcapitata and Chlorella sp. were compared on a time-averaged concentration (TAC) basis. Relationships were then derived between the exposure concentration and duration required to elicit different levels of toxicity expressed as inhibition concentration (IC). Continuous exposure IC50's of 3.0 and 1.9 μg/L were measured on a TAC basis for P. subcapitata and Chlorella sp., respectively. Algal growth rates generally recovered to control levels within 24-48 h of the copper pulse removal, with some treatments exhibiting significantly (p < 0.05) higher rates of cell division than controls in this recovery period. For both algae, when exposed to treatments with equivalent TACs, the continuous exposure elicited similar or slightly greater growth rate inhibition than the pulsed exposures. To elicit equivalent inhibition, the exposure concentration increased as the exposure duration decreased, and power models fitted this relationship reasonably well for both species. Water quality guideline values (WQGVs) are predominantly derived using data from continuous exposure toxicity bioassays, despite intermittent contaminant exposures often occurring in aquatic systems. The results indicate the WQGV for copper may be relaxed for pulsed exposures by a factor less than or equivalent to the TAC and still achieve a protection to these sensitive algae species.

Comparison of intermittent and continuous exposures to inorganic mercury in the mussel, Mytilus edulis: accumulation and sub-lethal physiological effects

Aquatic organisms are often subject to intermittent exposure to pollutants in real ecosystems. This study aimed to compare mercury accumulation and the physiological responses of mussels, Mytilus edulis during continuous and intermittent exposure to the metal. Mussels were treated in a semi-static, triplicated design to either a control (no added Hg) or 50 µg l(-1) Hg as HgCl2 in continuous (daily) or intermittent (2 day exposure, 2 days in clean seawater alternately) exposure for 14 days. A time-dependent increase in Hg accumulation was observed in the continuous exposure, while the intermittent treatment showed step-wise changes in Hg concentrations with the exposure profile, especially in the gills. At the end of the experiment, tissue Hg concentrations were significantly increased in the continuous compared to the intermittent exposure for digestive gland (4 fold), gonad and remaining soft tissue (>2 fold), but not for the gill and adductor muscle. There was no observed oxidative damage at the end of the experiment as measured by the thiobarbituric acid reactive substances (TBARS) concentrations in tissues from all treatments. However, total glutathione was significantly decreased in the gill and digestive gland of both the continuous and intermittent exposure by the end of the experiment. The neutral red retention ability of the haemocytes was not affected, but total haemocyte counts were significantly decreased (<2 fold) in the intermittent compared to the continuous exposure. Histopathological examinations showed less pathology in the gill, but more inflammation in the digestive gland of mussels for the intermittent compared to the continuous exposure. Overall, the results showed that Hg accumulation from intermittent exposure was less than that of the continuous exposure regime, but the sub-lethal responses are sometimes more severe than expected in the former.

Real exposure: field measurement of chemical plumes in headwater streams

In fluvial systems, organismic exposure to nonpoint source pollutants will fluctuate in frequency (exposure events), intensity (concentration), and duration. The reliance on lethal concentrations and static exposure in many laboratory studies does not adequately represent nor address exposure to in situ chemical plumes of fluvial habitats. To adequately address field exposure in a laboratory setting, one needs an understanding of the physics of chemical transmission within moving fluids. Because of the chaotic nature of turbulence, chemical plumes introduced to fluvial systems have a spatial and temporal microstructure with fluxes in chemical concentration. Consequently, time-averaged static exposure models are not ecologically relevant for the major reason of in situ distribution. The purpose of this study was to quantify in situ chemical distribution and dispersion within two physically different streams. Dopamine was introduced as a chemical tracer mimicking groundwater runoff. Chemical fluxes and stream hydrodynamics were simultaneously measured using a microelectrode and an acoustic Doppler velocimeter, respectively, at three heights of three downstream locations at each research site. Fine-scale measurements of the dopamine plume microstructure showed that organisms could be exposed to chemical fluctuations where concentrations are significantly greater than the overall time-averaged concentration. These measurements demonstrate that rather than relying on static exposure, standards for pollution must consider the concept of exposure being interdependently linked to flow of the fluid medium. The relationship between fluid dynamics, pollution exposure, and organism physiology are complex and must be evaluated in ways to mimic natural systems.

Coupled dynamics of energy budget and population growth of tilapia in response to pulsed waterborne copper

The impact of environmentally pulsed metal exposure on population dynamics of aquatic organisms remains poorly understood and highly unpredictable. The purpose of our study was to link a dynamic energy budget model to a toxicokinetic/toxicodynamic (TK/TD). We used the model to investigate tilapia population dynamics in response to pulsed waterborne copper (Cu) assessed with available empirical data. We mechanistically linked the acute and chronic bioassays of pulsed waterborne Cu at the scale of individuals to tilapia populations to capture the interaction between environment and population growth and reproduction. A three-stage matrix population model of larva-juvenile-adult was used to project offspring production through two generations. The estimated median population growth rate (λ) decreased from 1.0419 to 0.9991 under pulsed Cu activities ranging from 1.6 to 2.0 μg L(-1). Our results revealed that the influence on λ was predominately due to changes in the adult survival and larval survival and growth functions. We found that pulsed timing has potential impacts on physiological responses and population abundance. Our study indicated that increasing time intervals between first and second pulses decreased mortality and growth inhibition of tilapia populations, indicating that during long pulsed intervals tilapia may have enough time to recover. Our study concluded that the bioenergetics-based matrix population methodology could be employed in a life-cycle toxicity assessment framework to explore the effect of stage-specific mode-of-actions in population response to pulsed contaminants.