Is the toxicity of nanosized polymethylmethacrylate particles dependent on the exposure route and food items?

The environmental effects of nanoplastics-NPLs have been addressed mainly through short-term exposures to a few types of polymers, neglecting other NPLs that are economically relevant like polymethylmethacrylate - PMMA. This work aimed to assess long-term effects of PMMA-NPLs on the marine primary consumer Brachionus plicatilis, evaluating the influence of different exposure routes (waterborne, foodborne and both) and food items (Nannochloropsis gaditana and Tetraselmis chuii). Rotifers were 21 days exposed to: a) control, with clean medium and food-CTR; b) contaminated medium (8.1 mg PMMA-NPLs/L) and clean algae-MC; c) clean medium and contaminated algae (pre-incubated for 96 h on 8.1 mg PMMA-NPLs/L)-AC; and, d) contaminated medium and algae-MC/AC. Mortality (lx), total number of organisms (TN), fecundity (mx), populational growth rate (r), generational time (gt), and feeding rates were assessed. Effects on r and mx were found after 21 days. Organisms from AC had higher r than MC. MC/AC organisms performed better than control in all endpoints. Overall organisms fed with N. gaditana had higher TN, m_x and r than those fed with T. chuii. In the AC treatments, rotifers fed with N. gaditana had higher m_x. Results highlight that exposure route and food type may modulate NPLs' effects, supporting the need for standardization of assays.

Experimental muscle pain increases trapezius muscle activity during sustained isometric contractions of arm muscles

OBJECTIVE

In the present study, the influence of experimental muscle pain on muscle co-ordination and fatigue development during sustained isometric elbow flexion was investigated.

METHODS

Conventional surface electromyography (EMG) was recorded from the biceps brachii, brachioradialis, deltoideus and trapezius muscle during isometric elbow flexion at 40% maximum force. Single motor unit (MU) conduction velocity in the biceps brachii was assessed using a high spatial resolution surface EMG technique. Measurements were performed on 15 healthy subjects before, during and after (1) injection of hypertonic (pain condition) and (2) isotonic saline (control) into the biceps brachii. The pain intensity was assessed on a 10 cm visual analogue scale.

RESULTS

The experimental results showed in both experimental sessions a fatigue-related increase of the root mean square value of EMG (222+/-164% of the baseline), and a decrease of the median frequency (118+/-16% of the baseline) in all investigated muscles. A maximum pain level of in average 3.2 cm on the visual analogue scale was reached after injection of hypertonic saline during contraction. Differences between painful and control condition were seen in an increased trapezius activity (230+/-141%) during pain. The global EMG activity of the brachioradialis and biceps brachii was unaffected by experimental muscle pain in line with unaffected single MU conduction velocity in the biceps brachii. Differences in endurance time (mean 89.3 and 102.3 s, pain and control, respectively) were not significant.

CONCLUSIONS/SIGNIFICANCE

The findings suggest that upper extremity pain could be a possible source for overloading the trapezius muscle and as such is an important factor in occupational settings.