Short-term Exposure Periods Research Articles

Cold-water octocoral interactions with microplastics under laboratory conditions

Microplastic pollution is ubiquitous in the oceans, threatening the health of marine ecosystems. The deep sea is recognized as a sink for microplastics, but there is a paucity of information on how deep-sea organisms are being affected by this stressor. Considering their vulnerability to disturbance, this information is crucial to fully understand the need for conservation actions. Here, we develop a novel methodology to provide a detailed characterisation of the behavioural responses of the cold-water octocoral Viminella flagellum to microplastic exposure under laboratory conditions. Coral fragments were individually exposed to a concentration of 1500 items/L of fluorescent green polyethylene microspheres biofouled for three weeks, for a period of 24 h, and carefully monitored for the entire exposure period using high resolution time-lapse video. After exposure, each fragment was transferred to another tank, free of microplastics, and monitored for further 24 h. The coral fragments were dissected at the end of the experimental period to assess the number of microplastics that remained in the digestive tract of each polyp. Our results showed that during this short-term exposure period, V. flagellum was ingesting microspheres, but most importantly it demonstrated the capacity of egesting all particles within 24 h. These results are especially important when quantifying microplastic contamination in cold-water corals in their natural habitat, as only recently ingested microplastics may be detected, leading to potential underestimations of their exposure. Additionally, our results indicated that microplastics adhered to the coral tissue surface could be discarded through periodic shedding of the mucus. These observations suggest that cold-water octocorals can handle microplastics as they do with other foreign particles, although the cleaning mechanisms may require significant energy expenditures.

P070 ROLE OF NOVEL BLOOD PRESSURE METRICS IN EARLY BLOOD PRESSURE CONTROL ASSESSMENT: INSIGHTS FROM THE SPRINT TRIAL

Objective: Innovative blood pressure (BP) metrics is pivotal to expedite the BP management among individuals with hypertension. Methods and Findings: This is a post-hoc analysis of the SPRINT (Systolic Blood Pressure Intervention Trial). A total of 8369 participants, who had comprehensive BP records and experienced no adverse events during the initial 90-day follow-up, were included. Two novel BP metrics, systolic blood pressure (SBP) burden and Time-in-Target-Range (TTR), were calculated by employing three-month SBP recordings from follow-up data. SBP Burden were derived as the proportion of area under curve (AUC) over a specific SBP threshold (SBP values >130 mmHg) in a short-term exposure period (from the first month to third month). SBP TTR was estimated by the proportion of time in a specified SBP target range (110 to 140mmHg) in the same exposure period. Major adverse cardiovascular events (MACE), as the primary outcome of this analysis, was a composite endpoint including myocardial infarction, stroke, heart failure, and cardiovascular death. Secondary outcomes included individual components of the primary outcome, as well as all-cause mortality. The relationship of novel BP metrics and study endpoints was accessed by using adjusted Cox proportional hazards regression models. Over a median follow-up period of 3.90 [3.88-3.94] years, 559 MACEs occurred. Both SBP burden (Hazard Ratio [HR]: 1.126 [1.039-1.221]) and SBP TTR (HR: 0.862[0.783-0.949]) were independently correlated with MACEs according to adjusted Cox models. Evaluation using C-statistic and Net Reclassification Indexes (NRI) revealed that both two novel SBP metrics outperformed mean SBP and SBP standard deviation (SD) in predicting MACEs. Furthermore, the predictive value of SBP burden and TTR was consistent across MACE(P=0.383) and secondary endpoints (all P value > 0.05) in this analysis. Conclusions: Among non-diabetic patients with hypertension, both the cumulative SBP burden and TTR independently predict MACEs, surpassing the predictive power of mean SBP and SBP SD. This study substantiates the application of innovative BP measurements for early-stage assessment of BP control.

Investigating Long-Distance Transport of Perfluoroalkyl Acids in Wheat <em>via</em> a Split-Root Exposure Technique

Large amounts of perfluoroalkyl acids (PFAAs) have been introduced into the soil and accumulated by plants, posing potential risks to human health. It is imperative to investigate the accumulation and translocation of PFAAs within plants. Long-distance transport is an important pathway for PFAAs transferred from the plant leaves to the edible tissues through the phloem. However, it was previously difficult to assess the translocation potential of organic contamination in a short-term exposure period. The split-root experiment provides a solution to effectively uncover the long-distance translocation of PFAAs using a hydroponic experiment, which, in this study, was carried out in two 50 mL centrifuge tubes (A and B), of which centrifuge tube A had 50 mL of one-quarter strength Hoagland sterile nutrient solution, while centrifuge tube B had the same amount of nutrient concentration, and the target PFAAs (perfluorooctane sulfonic acid, PFOS, and perfluorooctane acid, PFOA) added at a given concentration. A whole wheat root was manually separated into two parts and inserted carefully into tubes A and B. The concentration of PFAAs in the roots, shoots of wheat, and solutions in tubes A and B were evaluated using LC-MS/MS, respectively, after being cultured in an incubator for 7 days and harvested. The results suggested that PFOA and PFOS experience a similar long-distance transport process through the phloem from the shoot to the root and could be released into the ambient environment. Thus, the split-root technique can be used to evaluate the long-distance transport of different chemicals.

Investigating Long-Distance Transport of Perfluoroalkyl Acids in Wheat via a Split-Root Exposure Technique.

Large amounts of perfluoroalkyl acids (PFAAs) have been introduced into the soil and accumulated by plants, posing potential risks to human health. It is imperative to investigate the accumulation and translocation of PFAAs within plants. Long-distance transport is an important pathway for PFAAs transferred from the plant leaves to the edible tissues through the phloem. However, it was previously difficult to assess the translocation potential of organic contamination in a short-term exposure period. The split-root experiment provides a solution to effectively uncover the long-distance translocation of PFAAs using a hydroponic experiment, which, in this study, was carried out in two 50 mL centrifuge tubes (A and B), of which centrifuge tube A had 50 mL of one-quarter strength Hoagland sterile nutrient solution, while centrifuge tube B had the same amount of nutrient concentration, and the target PFAAs (perfluorooctane sulfonic acid, PFOS, and perfluorooctane acid, PFOA) added at a given concentration. A whole wheat root was manually separated into two parts and inserted carefully into tubes A and B. The concentration of PFAAs in the roots, shoots of wheat, and solutions in tubes A and B were evaluated using LC-MS/MS, respectively, after being cultured in an incubator for 7 days and harvested. The results suggested that PFOA and PFOS experience a similar long-distance transport process through the phloem from the shoot to the root and could be released into the ambient environment. Thus, the split-root technique can be used to evaluate the long-distance transport of different chemicals.

Early-age mechanical properties and microstructures of Portland cement mortars containing different admixtures exposed to seawater

This study investigated the effects of seawater exposure on the mechanical, durability, and microstructural properties of cement mortars, which contained silica fume, metakaolin, or glass powder at two different replacement ratios. Test variables included the exposure conditions, exposure periods, supplementary cementitious material types, and replacement ratios. Compressive, flexural, and pull-off strengths were measured periodically. Mass change, water absorption, and rapid chloride permeability tests were conducted to evaluate the durability performance of Portland cement mortars (PCMs). Microcomputed tomography was utilized to obtain the pore information from representative PCMs. Test results revealed that seawater exposure yielded positive effects, including flexural strength and durability improvements during short-term exposure periods while those effects might not be last for long period. Metakaolin was the most effective supplementary cementitious material to minimize the reduction in compressive strength, while silica fume contributed to durability improvements. On the other hand, PCM containing GP did not show significant changes in strength and durability. Strong correlations between the flexural strength and durability were observed, and it was explained by additional hydration (i.e., matrix densification) of PCMs (except for the GP) due to the seawater curing which filled specific size of pores ranging 50–200 µm.

Environmental affected mechanical performance of additively manufactured carbon fiber–reinforced plastic composites

Due to their attractive strength-to-weight ratios, stiffness-to-weight ratios, thermal expansion, corrosion resistance, and vibration resistance properties, carbon fiber reinforced plastic (CFRP) composites have been widely used in applications ranging from aerospace to sporting goods. Considering some of the advantages of additive manufacturing (AM) over traditional subtractive methods, AM is being used to fabricate CFRP composites. For the fabrication method, several investigations have been conducted on materials and processing effects on the mechanical performance of the composites. However, no studies have investigated the effects of environmental conditions on mechanical performance. This study reports the environmental (temperature and relative humidity) affected mechanical performance of AM fabricated CFRP composites exposed to three different environmental conditions: warm–wet, warm–dry, and cold–dry, compared to samples tested immediately after fabrication under normal ambient conditions. The result was that the warm temperatures have insignificant effects on the mechanical performance of the composites, while near-zero degree cold temperatures have significant effects after the 96 h and 250 h short-term exposure periods. The result also showed the temperature to have more significant effects on mechanical properties than relative humidity. Under the warm conditions, the dry humidity resulted in a slight increase in material mechanical properties over the nominal ambient condition, while the wet humidity showed an insignificant reduction in material mechanical properties.

HISTOPATHOLOGICAL ALTERATIONS IN THE GILLS OF FRESH WATER FISH, LABEO ROHITA (HAMILTON-BUCHANAN) EXPOSED TO HEAVY METAL MIXTURE (Cd, Cr 8#x38; Pb)

Histopathological alterations are the changes arising in the tissues of the organisms after exposure to the certain pollutants. Histopathology has been widely used as biomarkers in the analysis of the health of fish exposed to pollutants. Thus they are recommended as useful biomarkers in eco-toxicological research, risk assessment and monitoring programs. The heavy metals like cadmium (Cd), chromium (Cr) and lead (Pb) are very toxic to animals which enter surface water from various sources. Fishes carry on in near contact with the water through their gills and thus liable to heavy metals exhausted from various sources. In this study, an effort has been made to assess the effect of heavy metal mixture on the gill tissues of Labeo rohita. The fresh water fish, labeo rohita were exposed to heavy metal mixture for short term exposure period (24, 48, 72 8#x38; 96 hours). After the stipulated period of exposure fishes were sacrificed and gills were isolated and used for histopathological studies. The important alterations in the tissues were noticed. Gill tissue found that degeneration of epithelial lining and fusion of primary lamellae.

Elucidating physiological and biochemical alterations in giant duckweed (Spirodela polyrhiza L. Schleiden) under diethyl phthalate stress: insights into antioxidant defence system.

BackgroundThe emollient properties of phthalates have led to their extensive production and intense use in plastic products. Owing to their weak covalent bonding with the plastic polymers, phthalates enter into the environment during their manufacturing, processing, disposal, consequently found their way directly into water sources, soil, and sediments.MethodsThe present study envisaged the toxic effects of diethyl phthalate (DEP) on physiological and biochemical attributes of Spirodela polyrhiza, when exposed to various concentrations of DEP (0, 10, 20, 40, 80, 100, 200, and 400 ppm) for short term exposure period of seven days.ResultsPlants of S. polyrhiza accumulated significant amount of DEP (112 mg kg−1 fw) when exposed to various concentrations of DEP for seven days. Results depicted that DEP toxicity significantly (p ≤ 0.05) affected growth parameters and pigments in treated S. polyrhiza as compared to control. Further, high doses of DEP (400 ppm) caused significant decrement in carbohydrate (86%), protein (76%) and elevation in MDA content (42%). Meanwhile, DEP altered the activities of antioxidant enzymes (SOD, CAT, APX, GPX and GR) along with the induction of enhanced levels of proline, electrolyte leakage and phenolic content. Scanning electron microscopic and confocal studies also confirmed oxidative stress in plants under DEP stress.ConclusionsPresent findings will help understand the accumulation, tolerance, and detoxification mechanisms of DEP by S. polyrhiza to counteract the effects of reactive oxygen species (ROS), along with the evaluation of environmental threat for aquatic plants in aquatic ecosystems.

Metabolic recovery and compensatory shell growth of juvenile Pacific geoduck Panopea generosa following short-term exposure to acidified seawater.

While acute stressors can be detrimental, environmental stress conditioning can improve performance. To test the hypothesis that physiological status is altered by stress conditioning, we subjected juvenile Pacific geoduck, Panopea generosa, to repeated exposures of elevated pCO2 in a commercial hatchery setting followed by a period in ambient common garden. Respiration rate and shell length were measured for juvenile geoduck periodically throughout short-term repeated reciprocal exposure periods in ambient (~550 μatm) or elevated (~2400 μatm) pCO2 treatments and in common, ambient conditions, 5 months after exposure. Short-term exposure periods comprised an initial 10-day exposure followed by 14 days in ambient before a secondary 6-day reciprocal exposure. The initial exposure to elevated pCO2 significantly reduced respiration rate by 25% relative to ambient conditions, but no effect on shell growth was detected. Following 14 days in common garden, ambient conditions, reciprocal exposure to elevated or ambient pCO2 did not alter juvenile respiration rates, indicating ability for metabolic recovery under subsequent conditions. Shell growth was negatively affected during the reciprocal treatment in both exposure histories; however, clams exposed to the initial elevated pCO2 showed compensatory growth with 5.8% greater shell length (on average between the two secondary exposures) after 5 months in ambient conditions. Additionally, clams exposed to the secondary elevated pCO2 showed 52.4% increase in respiration rate after 5 months in ambient conditions. Early exposure to low pH appears to trigger carryover effects suggesting bioenergetic re-allocation facilitates growth compensation. Life stage-specific exposures to stress can determine when it may be especially detrimental, or advantageous, to apply stress conditioning for commercial production of this long-lived burrowing clam.

A combined toxicokinetics and toxicodynamics approach to investigate delayed lead toxicity in the soil invertebrate Enchytraeus crypticus

In a previous study, Pb toxicity was found to be delayed compared to Pb bioaccumulation in Enchytraeus crypticus. This study aimed at further investigating the acute and delayed onset of Pb toxicity in E. crypticus by using a combination of toxicokinetics and toxicodynamics approaches. Enchytraeids were exposed to different Pb concentrations (uptake phase) in natural LUFA 2.2 soil for different short-term exposure periods, followed by a 7-d elimination phase in clean soils. Body Pb concentrations and enchytraeid mortality were determined at different time intervals during both the exposure and the elimination phase. Pb uptake kinetics in E. crypticus were well described by a three-stage first-order model with an initial overshoot in body Pb concentrations. At higher exposure concentrations, Pb caused delayed enchytraeid mortality even following short-term exposure. LC50 based on body Pb concentrations appeared no good descriptor of delayed Pb toxicity in E. crypticus. Exposure time had a major impact on Pb bioaccumulation, toxicity and its delayed effects, which argues against relying on ecotoxicity tests for metal toxicity using a fix exposure duration. The presence of delayed toxic effects also suggests that post-exposure observations are necessary to avoid underestimation of metal toxicity.

Sub-lethal and lethal toxicities of elevated CO2 on embryonic, juvenile, and adult stages of marine medaka Oryzias melastigma

The potential leakage from marine CO2 storage sites is of increasing concern, but few studies have evaluated the probable adverse effects on marine organisms. Fish, one of the top predators in marine environments, should be an essential representative species used for water column toxicity testing in response to waterborne CO2 exposure. In the present study, we conducted fish life cycle toxicity tests to fully elucidate CO2 toxicity mechanism effects. We tested sub-lethal and lethal toxicities of elevated CO2 concentrations on marine medaka (Oryzias melastigma) at different developmental stages. At each developmental stage, the test species was exposed to varying concentrations of gaseous CO2 (control air, 5%, 10%, 20%, and 30%), with 96 h of exposure at 0–4 d (early stage), 4–8 d (middle stage), and 8–12 d (late stage). Sub-lethal and lethal effects, including early developmental delays, cardiac edema, tail abnormalities, abnormal pigmentation, and mortality were monitored daily during the 14 d exposure period. At the embryonic stage, significant sub-lethal and lethal effects were observed at pH < 6.30. Hypercapnia can cause long-term and/or delayed developmental embryonic problems, even after transfer back to clean seawater. At fish juvenile and adult stages, significant mortality was observed at pH < 5.70, indicating elevated CO2 exposure might cause various adverse effects, even during short-term exposure periods. It should be noted the early embryonic stage was found more sensitive to CO2 exposure than other developmental stages of the fish life cycle. Overall, the present study provided baseline information for potential adverse effects of high CO2 concentration exposure on fish developmental processes at different life cycle stages in marine ecosystems.

Temporarily occupied space with metabolic-rate-initiated thermal overshoots—A case study in railway stations in transition seasons

Temporarily occupied space (TOS) is defined as an air-conditioned space in which most of occupants stay for less than a certain period (e.g., 40 min), such as post offices, supermarkets, bookstores, and banks. The definition mainly emphasizes two aspects: obvious temperature step up/down and short-term exposure periods. Typical TOSs with predominantly temperature-initiated thermal overshoots have been explored in previous studies. Indeed, apart from temperature-initiated thermal overshoots, thermal overshoots can also be initiated by other parameters, such as metabolic rates. In this view, the definition of thermal overshoots was generalized and a case study was conducted at high-speed railway station in China under conditions of transition seasons. The phenomenon of metabolic-rate-initiated thermal overshoots instead of temperature-initiated thermal overshoots was observed and explored, based on objective measurements and subjective questionnaire surveys. The results could optimize the design and operation of air conditioning and mechanical ventilation (ACMV) systems in such TOSs as embodied by railway stations. In addition, the probit analysis method for analyzing neutral temperature ranges instead of neutral temperature points was also discussed.

Dioxin and phthalate uptake and assimilation by the green mussel Perna viridis

In this study, the aqueous uptake and dietary assimilation (trophic transfer) of two endocrine disrupting compounds (dioxin and phathalic acid) in the green mussel Perna viridis were quantified. During short-term exposure period, dioxin rapidly sorbed onto phytoplankton and its accumulation was much higher than that of phthalate. The uptake of these two compounds by the mussels increased with increasing temperature and salinity (for dioxin only). The dietary assimilation of the two contaminants was rather modest (10–64% for dioxin and 20–47% for phthalate), and was greatly dependent on the food species and concentration. Interestingly, dietary assimilation increased with increasing diatom food concentration. Gut passage time was partially responsible for the variable dietary assimilation. Given the high dissolved uptake rate and the modest dietary assimilation, aqueous exposure was predicted to be the dominant bioaccumulation source for both dioxin and phthalate in the green mussels under most conditions.

Workplace exposure to nanoparticles and the application of provisional nanoreference values in times of uncertain risks

Nano reference values (NRVs) for occupational use of nanomaterials were tested as provisional substitute for Occupational Exposure Limits (OELs). NRVs can be used as provisional limit values until Health-Based OELs or derived no-effect levels (DNEL) become available. NRVs were defined for 8 h periods (time weighted average) and for short-term exposure periods (15 min-time weighted average). To assess the usefulness of these NRVs, airborne number concentrations of nanoparticles (NPs) in the workplace environment were measured during paint manufacturing, electroplating, light equipment manufacturing, non-reflective glass production, production of pigment concentrates and car refinishing. Activities monitored were handling of solid engineered NPs (ENP), abrasion, spraying and heating during occupational use of nanomaterials (containing ENPs) and machining nanosurfaces. The measured concentrations are often presumed to contain ENPs as well as process-generated NPs (PGNP). The PGNP are found to be a significant source for potential exposure and cannot be ignored in risk assessment. Levels of NPs identified in workplace air were up to several millions of nanoparticles/cm3. Conventional components in paint manufacturing like CaCO3 and talc may contain a substantial amount of nanosized particulates giving rise to airborne nanoparticle concentrations. It is argued that risk assessments carried out for e.g. paint manufacturing processes using conventional non-nano components should take into account potential nanoparticle emissions as well. The concentrations measured were compared with particle-based NRVs and with mass-based values that have also been proposed for workers protection. It is concluded that NRVs can be used for risk management for handling or processing of nanomaterials at workplaces provided that the scope of NRVs is not limited to ENPs only, but extended to the exposure to process-generated NPs as well.

Erratum to: Histological changes in the liver of reared spotted scat (Scatophagus argus L.) after exposure to mercury

The toxic effects of mercury (Hg) on the histology of the liver of reared spotted scat (Scatophagus argus L.) were investigated. The experiment was conducted to identify the effect of metal concentrations and exposure period on degrees and nature of histological changes in the liver of exposed fish. Selected fish were exposed to 10, 20, and 30 μg L−1 concentrations of mercury over short-term exposure period. Similar histological changes occurred in the livers of specimens exposed to 10, 20, and 30 μg L−1 concentrations, indicating a definite toxic response to all metal concentrations. These histological changes included hyalinization, hepatocyte vacuolation, cellular swelling, necrosis, vacuolar degeneration, and congestion of blood vessels. The intensity of these histological changes was, however, influenced by the extent of the exposure period.

Effect of preservatives on ciliary beat frequency in human nasal epithelial cell culture: Single versus multiple exposure

As preservatives may impair mucociliary clearance, we wanted to systematically study their time-dependent effect on the ciliary beat frequency (CBF) in human nasal epithelial cells (HNEC). CBF was determined using a high-speed digital imaging method. Five preservatives were selected including benzalkonium chloride, phenylethyl alcohol, methylparaben, propylparaben and chlorbutol. We were interested in the effect of these preservatives on CBF after single and repetitive exposure. Methylparaben (0.0033%), propylparaben (0.0017%) and chlorbutol (0.005%) did not impair CBF, neither after a single short-term exposure period, nor after a single long-term exposure period. Long-term exposure to benzalkonium chloride (0.001%), phenylethyl alcohol (0.125%) and a combination of methyl- and propylparaben (0.0033 and 0.0017%) significantly decreased CBF. After a short-term exposure period, CBF recovered for phenylethyl alcohol and the combination of methyl- and propylparaben. Benzalkonium chloride decreased CBF non-reversibly. For two compounds, the effect on CBF was evaluated after repetitive exposure during 15 min for 5 consecutive days. Benzalkonium chloride resulted in ciliostasis for all concentrations tested after 5 days. Phenylethyl alcohol revealed a concentration-dependent effect on CBF, but no ciliostasis was observed. In conclusion, methylparaben, propylparaben and chlorbutol can be considered as cilio-friendly. Repetitive exposure revealed a cumulative effect on CBF for benzalkonium chloride and phenylethyl alcohol.

Trace metal ingestion and assimilation by the green mussel Perna viridis in a phytoplankton and sediment mixture

We examined trace metal ingestion and assimilation (Cd, Se, Zn) by the green mussel Perna viridis in a mixture of diatoms and sediment at concentrations below and above the pseudofeces production levels. Dual gamma radiotracers (109Cd, 65Zn) were used to investigate particle selection on marine diatoms and sediments. The diatom (Thalassiosira weissflogii) was radiolabeled with 109Cd, and the natural sediment was radiolabeled with 65Zn. By comparing the ratios of 109Cd:65Zn in the particle mixture, mussel tissues and pseudofeces within a short-term exposure period (35 min), the results demonstrated that the green mussels were able to selectively ingest the diatom particles at a high particle load. Efficiency of selection for nutritious particles (e.g. diatoms) increased with increasing ratio of sediments in the particle mixture. Pseudofeces contained a higher ratio of sediments relative to that in the feeding suspension. No major particle selection was observed at concentrations below the level for pseudofeces production. The assimilation of Cd, Se and Zn by the green mussels was quantified using a pulse-chase feeding technique. The assimilation of Se and Zn by the green mussels from ingested diatoms was reduced with the presence of sediment within the mussel gut, presumably due to the resorption of metals onto the sediment, leading to a quicker passage of metals through the digestive tract and a lower proportion of metals subjected to intensive digestion. In contrast, the presence of diatoms did not significantly affect metal assimilation from ingested sediment. A significant correlation between metal assimilation efficiency and metal gut passage time was also observed. Metal assimilation by the green mussels appeared to be little dependent on the particle concentration in seawater. Our study suggests that particle selection may potentially alter metal influx from ingested food sources, particularly at high particle concentrations. Selective feeding of nutritious particles, coupled with a high assimilation efficiency from these ingested particles, may increase metal influx into mussels from the dietary phase.

Responses of Zn assimilation by coastal plankton to macronutrients

We examined the Zn uptake in marine diatoms and its transfer to marine copepods under different nutrient‐replete and ‐deplete conditions. Zn uptake, quantified by measurements of both total cellular and intracellular Zn accumulation in two coastal diatoms (Thalassiosira pseudonana and Thalassiosira weissflogii), was greatly dependent on the ambient nitrogen conditions. Semicontinuous culture experiments demonstrated that diatom cells accumulated much less Zn with decreasing ambient nitrate concentration. The calculated Zn uptake rate decreased by 1.8 times in T. pseudonana and 1.5 times in T. weissflogii with a decrease in ambient N concentration from 176 µM to 17.6 µM. N‐starved cells also accumulated much less Zn compared with N‐enriched cells. The uptake rate decreased by 2.5–2.6 times when both diatoms were starved of N for 2 d. The intracellular partitioning of Zn in the diatom T. pseudonana was positively related to the ambient N level within the short‐term exposure period (5 h). P starvation, however, resulted in an increase in Zn accumulation in the diatoms, whereas Si starvation did not significantly affect the rate of Zn uptake in diatoms. The trophic transfer was quantified by measurement of Zn assimilation efficiency in two copepods (Calanus sinicus and Acartia spinicauda) feeding on diatoms with a different N quota. Assimilation generally increased with an increase in the N quota of the diatoms. In one experiment (C. sinicus feeding on diatom T. weissflogii), the influence of different N status in diatoms on Zn assimilation by copepods was statistically significant. In contrast, the elimination rate (physiological turnover rate) was independent of the N quota of the cells. Nitrogen enrichment may lead to an increase in Zn uptake and transfer in marine plankton. Our study therefore suggests that there is considerable interaction between macronutrients and Zn uptake by plankton in aquatic systems.

Metal uptake in a coastal diatom influenced by major nutrients (N, P, and Si)

The influence of major nutrient additions on trace metal uptake (Cd, Se, and Zn) in a coastal diatom Thalassiosira pseudonana was investigated. A short-term exposure (5 h) was employed to measure the concentration factor (ratio of metal concentration in the cells to metal concentration in the medium) which was used as a kinetic parameter to quantify the relative rate of metal uptake in the cells. Following an initial rapid surface sorption, a linear pattern of uptake over time was typical for Cd, Se and Zn, indicating that these metals may have been transported intracellularly during the short-term exposure period. N addition significantly increased the rates of Cd uptake in the cells. Although the concentration factor of Zn increased with N addition, statistical analysis indicated that N addition did not significantly affect the rate of Zn uptake in the cells. Se uptake in the cells was independent of N additions, but was lowered with increasing Si concentration. Si addition did not significantly affect Cd and Zn uptake. Similarly, P addition did not influence the rates of metal uptake in the cells. There was a significant correlation between the rate of uptake of Cd and Zn and the cell growth rate. This study demonstrated that water quality brought about by a change in nutrient condition could considerably influence the uptake of metals by marine phytoplankton.

Induction of hepatic tumors with 7,12-dimethylbenz[ a]anthracene in two species of viviparous fishes (genus Poeciliopsis)

Liver neoplasms were induced in two species of viviparous fishes, Poeciliopsis lucida and P. monacha, by repeated short-term exposures to an aqueous suspension of 5 ppm 7,12-dimethylbenz[ a]anthracene (DMBA). Predominantly hepatocellular neoplasms developed in 47 out of 106 fish surviving the period allowed for tumor development, 6–9 months after initial exposure to DMBA. The use of short-term exposure periods of 6 hr in young fish and up to 20 hr in adults reduced stress and mortalities caused by the toxicity of DMBA at 5 ppm. A lower concentration of DMBA, 0.25 ppm, failed to induce tumors in any of the surviving 230 of 295 young fish administered repeated 20-hr exposures. This study shows for the first time that DMBA is carcinogenic to fish.